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 $86.93   12.182%   $97.5198   $97.52   $97.50   $97.50  
  Purchase #2 $92.82   7.798%   $100.0581   $100.06   $100.05   $100.10  
  Purchase #3 $110.31   12.297%   $123.8748   $123.87   $123.85   $123.90  
  Purchase #4 $208.78   9.177%   $227.9397   $227.94   $227.95   $227.90  
  Purchase #5 $217.65   8.593%   $236.3527   $236.35   $236.35   $236.40  
  Purchase #6 $155.37   10.202%   $171.2208   $171.22   $171.20   $171.20  
  Purchase #7 $200.31   6.623%   $213.5765   $213.58   $213.60   $213.60  
  7 purchase totals = $1,072.17       $1,170.5424   $1,170.54   $1,170.50   $1,170.60