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 $85.71   13.784%   $97.5243   $97.52   $97.50   $97.50  
  Purchase #2 $9.62   5.126%   $10.1131   $10.11   $10.10   $10.10  
  Purchase #3 $84.39   13.764%   $96.0054   $96.01   $96.00   $96.00  
  Purchase #4 $236.73   10.281%   $261.0682   $261.07   $261.05   $261.10  
  Purchase #5 $94.58   11.407%   $105.3687   $105.37   $105.35   $105.40  
  Purchase #6 $194.26   5.238%   $204.4353   $204.44   $204.45   $204.40  
  Purchase #7 $240.82   4.262%   $251.0837   $251.08   $251.10   $251.10  
  7 purchase totals = $946.11       $1,025.5987   $1,025.60   $1,025.55   $1,025.60