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 $89.57   4.492%   $93.5935   $93.59   $93.60   $93.60  
  Purchase #2 $245.41   12.340%   $275.6936   $275.69   $275.70   $275.70  
  Purchase #3 $105.32   9.242%   $115.0537   $115.05   $115.05   $115.10  
  Purchase #4 $220.26   13.174%   $249.2771   $249.28   $249.30   $249.30  
  Purchase #5 $152.55   4.811%   $159.8892   $159.89   $159.90   $159.90  
  Purchase #6 $124.40   11.181%   $138.3092   $138.31   $138.30   $138.30  
  Purchase #7 $243.80   12.485%   $274.2384   $274.24   $274.25   $274.20  
  7 purchase totals = $1,181.31       $1,306.0547   $1,306.05   $1,306.10   $1,306.10