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 $134.55   12.395%   $151.2275   $151.23   $151.25   $151.20  
  Purchase #2 $55.57   9.226%   $60.6969   $60.70   $60.70   $60.70  
  Purchase #3 $80.46   6.853%   $85.9739   $85.97   $85.95   $86.00  
  Purchase #4 $192.44   9.193%   $210.131   $210.13   $210.15   $210.10  
  Purchase #5 $136.76   4.718%   $143.2123   $143.21   $143.20   $143.20  
  Purchase #6 $33.95   10.215%   $37.418   $37.42   $37.40   $37.40  
  Purchase #7 $119.55   5.262%   $125.8407   $125.84   $125.85   $125.80  
  7 purchase totals = $753.28       $814.5003   $814.50   $814.50   $814.40