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 $52.92   12.172%   $59.3614   $59.36   $59.35   $59.40  
  Purchase #2 $67.25   8.527%   $72.9844   $72.98   $73.00   $73.00  
  Purchase #3 $214.79   13.260%   $243.2712   $243.27   $243.25   $243.30  
  Purchase #4 $197.85   5.540%   $208.8109   $208.81   $208.80   $208.80  
  Purchase #5 $85.95   3.299%   $88.7855   $88.79   $88.80   $88.80  
  Purchase #6 $221.30   6.432%   $235.534   $235.53   $235.55   $235.50  
  Purchase #7 $59.51   10.867%   $65.977   $65.98   $66.00   $66.00  
  7 purchase totals = $899.57       $974.7244   $974.72   $974.75   $974.80