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 $112.88   8.258%   $122.2016   $122.20   $122.20   $122.20  
  Purchase #2 $189.39   3.313%   $195.6645   $195.66   $195.65   $195.70  
  Purchase #3 $68.97   3.396%   $71.3122   $71.31   $71.30   $71.30  
  Purchase #4 $56.34   6.560%   $60.0359   $60.04   $60.05   $60.00  
  Purchase #5 $249.53   9.414%   $273.0208   $273.02   $273.00   $273.00  
  Purchase #6 $220.78   3.337%   $228.1474   $228.15   $228.15   $228.10  
  Purchase #7 $24.37   7.479%   $26.1926   $26.19   $26.20   $26.20  
  7 purchase totals = $922.26       $976.5750   $976.57   $976.55   $976.50