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 $208.48   12.342%   $234.2106   $234.21   $234.20   $234.20  
  Purchase #2 $88.80   5.507%   $93.6902   $93.69   $93.70   $93.70  
  Purchase #3 $181.28   9.703%   $198.8696   $198.87   $198.85   $198.90  
  Purchase #4 $25.64   4.495%   $26.7925   $26.79   $26.80   $26.80  
  Purchase #5 $83.31   11.108%   $92.5641   $92.56   $92.55   $92.60  
  Purchase #6 $187.56   4.175%   $195.3906   $195.39   $195.40   $195.40  
  Purchase #7 $34.35   12.798%   $38.7461   $38.75   $38.75   $38.70  
  7 purchase totals = $809.42       $880.2637   $880.26   $880.25   $880.30