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 $32.62   13.428%   $37.0002   $37.00   $37.00   $37.00  
  Purchase #2 $114.59   12.261%   $128.6399   $128.64   $128.65   $128.60  
  Purchase #3 $101.88   9.106%   $111.1572   $111.16   $111.15   $111.20  
  Purchase #4 $243.35   6.685%   $259.6179   $259.62   $259.60   $259.60  
  Purchase #5 $171.64   6.118%   $182.1409   $182.14   $182.15   $182.10  
  Purchase #6 $144.51   8.778%   $157.1951   $157.20   $157.20   $157.20  
  Purchase #7 $66.28   12.433%   $74.5206   $74.52   $74.50   $74.50  
  7 purchase totals = $874.87       $950.2718   $950.28   $950.25   $950.20