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 $224.29   10.868%   $248.6658   $248.67   $248.65   $248.70  
  Purchase #2 $74.86   10.496%   $82.7173   $82.72   $82.70   $82.70  
  Purchase #3 $113.89   10.479%   $125.8245   $125.82   $125.80   $125.80  
  Purchase #4 $50.42   5.297%   $53.0907   $53.09   $53.10   $53.10  
  Purchase #5 $232.64   9.206%   $254.0568   $254.06   $254.05   $254.10  
  Purchase #6 $124.62   13.146%   $141.0025   $141.00   $141.00   $141.00  
  Purchase #7 $211.99   11.805%   $237.0154   $237.02   $237.00   $237.00  
  7 purchase totals = $1,032.71       $1,142.3730   $1,142.38   $1,142.30   $1,142.40