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 $46.41   10.841%   $51.4413   $51.44   $51.45   $51.40  
  Purchase #2 $26.94   10.779%   $29.8439   $29.84   $29.85   $29.80  
  Purchase #3 $248.58   5.579%   $262.4483   $262.45   $262.45   $262.40  
  Purchase #4 $60.84   8.443%   $65.9767   $65.98   $66.00   $66.00  
  Purchase #5 $108.87   5.838%   $115.2258   $115.23   $115.25   $115.20  
  Purchase #6 $211.89   5.198%   $222.904   $222.90   $222.90   $222.90  
  Purchase #7 $52.44   11.454%   $58.4465   $58.45   $58.45   $58.40  
  7 purchase totals = $755.97       $806.2865   $806.29   $806.35   $806.10