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 $185.32   6.479%   $197.3269   $197.33   $197.35   $197.30  
  Purchase #2 $137.52   10.762%   $152.3199   $152.32   $152.30   $152.30  
  Purchase #3 $240.34   11.648%   $268.3348   $268.33   $268.35   $268.30  
  Purchase #4 $59.81   8.824%   $65.0876   $65.09   $65.10   $65.10  
  Purchase #5 $231.83   11.482%   $258.4487   $258.45   $258.45   $258.40  
  Purchase #6 $206.92   7.683%   $222.8177   $222.82   $222.80   $222.80  
  Purchase #7 $235.93   10.472%   $260.6366   $260.64   $260.65   $260.60  
  7 purchase totals = $1,297.67       $1,424.9722   $1,424.98   $1,425.00   $1,424.80