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 $63.76   5.397%   $67.2011   $67.20   $67.20   $67.20  
  Purchase #2 $249.57   10.446%   $275.6401   $275.64   $275.65   $275.60  
  Purchase #3 $22.56   7.466%   $24.2443   $24.24   $24.25   $24.20  
  Purchase #4 $180.64   10.655%   $199.8872   $199.89   $199.90   $199.90  
  Purchase #5 $78.73   10.496%   $86.9935   $86.99   $87.00   $87.00  
  Purchase #6 $170.37   5.767%   $180.1952   $180.20   $180.20   $180.20  
  Purchase #7 $147.78   11.180%   $164.3018   $164.30   $164.30   $164.30  
  7 purchase totals = $913.41       $998.4632   $998.46   $998.50   $998.40