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 $54.84   7.506%   $58.9563   $58.96   $58.95   $59.00  
  Purchase #2 $200.56   3.286%   $207.1504   $207.15   $207.15   $207.20  
  Purchase #3 $180.47   11.507%   $201.2367   $201.24   $201.25   $201.20  
  Purchase #4 $233.61   5.221%   $245.8068   $245.81   $245.80   $245.80  
  Purchase #5 $21.67   12.373%   $24.3512   $24.35   $24.35   $24.40  
  Purchase #6 $140.77   13.274%   $159.4558   $159.46   $159.45   $159.50  
  Purchase #7 $61.39   6.543%   $65.4067   $65.41   $65.40   $65.40  
  7 purchase totals = $893.31       $962.3639   $962.38   $962.35   $962.50