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 $59.75   8.618%   $64.8993   $64.90   $64.90   $64.90  
  Purchase #2 $115.64   5.484%   $121.9817   $121.98   $122.00   $122.00  
  Purchase #3 $240.81   6.742%   $257.0454   $257.05   $257.05   $257.00  
  Purchase #4 $55.36   5.803%   $58.5725   $58.57   $58.55   $58.60  
  Purchase #5 $106.57   8.710%   $115.8522   $115.85   $115.85   $115.90  
  Purchase #6 $33.84   6.254%   $35.9564   $35.96   $35.95   $36.00  
  Purchase #7 $73.45   9.226%   $80.2265   $80.23   $80.25   $80.20  
  7 purchase totals = $685.42       $734.5340   $734.54   $734.55   $734.60