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 $61.52   10.860%   $68.2011   $68.20   $68.20   $68.20  
  Purchase #2 $194.82   8.425%   $211.2336   $211.23   $211.25   $211.20  
  Purchase #3 $250.56   7.304%   $268.8609   $268.86   $268.85   $268.90  
  Purchase #4 $100.97   8.554%   $109.607   $109.61   $109.60   $109.60  
  Purchase #5 $18.73   8.602%   $20.3412   $20.34   $20.35   $20.30  
  Purchase #6 $123.39   6.439%   $131.3351   $131.34   $131.35   $131.30  
  Purchase #7 $152.27   4.412%   $158.9882   $158.99   $159.00   $159.00  
  7 purchase totals = $902.26       $968.5671   $968.57   $968.60   $968.50