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 $167.53   5.158%   $176.1712   $176.17   $176.15   $176.20  
  Purchase #2 $136.70   9.183%   $149.2532   $149.25   $149.25   $149.30  
  Purchase #3 $206.91   7.394%   $222.2089   $222.21   $222.20   $222.20  
  Purchase #4 $112.96   11.866%   $126.3638   $126.36   $126.35   $126.40  
  Purchase #5 $126.30   8.823%   $137.4434   $137.44   $137.45   $137.40  
  Purchase #6 $242.69   13.481%   $275.407   $275.41   $275.40   $275.40  
  Purchase #7 $159.77   6.179%   $169.6422   $169.64   $169.65   $169.60  
  7 purchase totals = $1,152.86       $1,256.4897   $1,256.48   $1,256.45   $1,256.50