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 $61.75   3.761%   $64.0724   $64.07   $64.05   $64.10  
  Purchase #2 $123.80   6.694%   $132.0872   $132.09   $132.10   $132.10  
  Purchase #3 $219.73   10.794%   $243.4477   $243.45   $243.45   $243.40  
  Purchase #4 $116.67   8.389%   $126.4574   $126.46   $126.45   $126.50  
  Purchase #5 $230.65   13.164%   $261.0128   $261.01   $261.00   $261.00  
  Purchase #6 $194.57   4.602%   $203.5241   $203.52   $203.50   $203.50  
  Purchase #7 $196.47   10.416%   $216.9343   $216.93   $216.95   $216.90  
  7 purchase totals = $1,143.64       $1,247.5359   $1,247.53   $1,247.50   $1,247.50