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 $60.52   11.391%   $67.4138   $67.41   $67.40   $67.40  
  Purchase #2 $155.96   3.831%   $161.9348   $161.93   $161.95   $161.90  
  Purchase #3 $109.78   13.646%   $124.7606   $124.76   $124.75   $124.80  
  Purchase #4 $229.80   13.121%   $259.9521   $259.95   $259.95   $260.00  
  Purchase #5 $153.74   4.438%   $160.563   $160.56   $160.55   $160.60  
  Purchase #6 $48.80   11.256%   $54.2929   $54.29   $54.30   $54.30  
  Purchase #7 $54.61   4.523%   $57.08   $57.08   $57.10   $57.10  
  7 purchase totals = $813.21       $885.9972   $885.98   $886.00   $886.10