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 $94.37   10.477%   $104.2571   $104.26   $104.25   $104.30  
  Purchase #2 $200.68   6.204%   $213.1302   $213.13   $213.15   $213.10  
  Purchase #3 $122.29   9.492%   $133.8978   $133.90   $133.90   $133.90  
  Purchase #4 $24.92   9.667%   $27.329   $27.33   $27.35   $27.30  
  Purchase #5 $178.49   9.211%   $194.9307   $194.93   $194.95   $194.90  
  Purchase #6 $26.72   7.395%   $28.6959   $28.70   $28.70   $28.70  
  Purchase #7 $63.71   12.544%   $71.7018   $71.70   $71.70   $71.70  
  7 purchase totals = $711.18       $773.9425   $773.95   $774.00   $773.90