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 $118.34   7.499%   $127.2143   $127.21   $127.20   $127.20  
  Purchase #2 $146.86   6.709%   $156.7128   $156.71   $156.70   $156.70  
  Purchase #3 $105.78   13.154%   $119.6943   $119.69   $119.70   $119.70  
  Purchase #4 $234.46   13.135%   $265.2563   $265.26   $265.25   $265.30  
  Purchase #5 $33.58   3.797%   $34.855   $34.86   $34.85   $34.90  
  Purchase #6 $145.96   4.146%   $152.0115   $152.01   $152.00   $152.00  
  Purchase #7 $75.25   12.612%   $84.7405   $84.74   $84.75   $84.70  
  7 purchase totals = $860.23       $940.4847   $940.48   $940.45   $940.50