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 $205.86   4.251%   $214.6111   $214.61   $214.60   $214.60  
  Purchase #2 $60.61   5.775%   $64.1102   $64.11   $64.10   $64.10  
  Purchase #3 $108.56   12.387%   $122.0073   $122.01   $122.00   $122.00  
  Purchase #4 $191.43   10.299%   $211.1454   $211.15   $211.15   $211.10  
  Purchase #5 $167.27   4.629%   $175.0129   $175.01   $175.00   $175.00  
  Purchase #6 $108.54   12.235%   $121.8199   $121.82   $121.80   $121.80  
  Purchase #7 $66.90   4.873%   $70.16   $70.16   $70.15   $70.20  
  7 purchase totals = $909.17       $978.8668   $978.87   $978.80   $978.80