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 $84.55   12.331%   $94.9759   $94.98   $95.00   $95.00  
  Purchase #2 $187.93   6.819%   $200.7449   $200.74   $200.75   $200.70  
  Purchase #3 $133.29   12.807%   $150.3605   $150.36   $150.35   $150.40  
  Purchase #4 $23.90   8.396%   $25.9066   $25.91   $25.90   $25.90  
  Purchase #5 $159.91   8.256%   $173.1122   $173.11   $173.10   $173.10  
  Purchase #6 $71.89   6.537%   $76.5894   $76.59   $76.60   $76.60  
  Purchase #7 $179.41   11.743%   $200.4781   $200.48   $200.50   $200.50  
  7 purchase totals = $840.88       $922.1676   $922.17   $922.20   $922.20