Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $225.36   11.388%   $251.024   $251.02   $251.00   $251.00  
  Purchase #2 $152.67   8.108%   $165.0485   $165.05   $165.05   $165.00  
  Purchase #3 $205.95   12.465%   $231.6217   $231.62   $231.60   $231.60  
  Purchase #4 $192.86   5.259%   $203.0025   $203.00   $203.00   $203.00  
  Purchase #5 $186.82   13.631%   $212.2854   $212.29   $212.30   $212.30  
  Purchase #6 $110.93   5.776%   $117.3373   $117.34   $117.35   $117.30  
  Purchase #7 $239.77   3.439%   $248.0157   $248.02   $248.00   $248.00  
  7 purchase totals = $1,314.36       $1,428.3351   $1,428.34   $1,428.30   $1,428.20