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 $91.30   12.227%   $102.4633   $102.46   $102.45   $102.50  
  Purchase #2 $106.71   13.129%   $120.72   $120.72   $120.70   $120.70  
  Purchase #3 $66.95   8.632%   $72.7291   $72.73   $72.75   $72.70  
  Purchase #4 $186.40   3.675%   $193.2502   $193.25   $193.25   $193.30  
  Purchase #5 $240.80   3.109%   $248.2865   $248.29   $248.30   $248.30  
  Purchase #6 $215.60   4.363%   $225.0066   $225.01   $225.00   $225.00  
  Purchase #7 $227.33   9.222%   $248.2944   $248.29   $248.30   $248.30  
  7 purchase totals = $1,135.09       $1,210.7501   $1,210.75   $1,210.75   $1,210.80