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 $46.61   12.526%   $52.4484   $52.45   $52.45   $52.40  
  Purchase #2 $185.51   4.659%   $194.1529   $194.15   $194.15   $194.20  
  Purchase #3 $72.33   4.496%   $75.582   $75.58   $75.60   $75.60  
  Purchase #4 $175.57   7.723%   $189.1293   $189.13   $189.15   $189.10  
  Purchase #5 $163.56   12.810%   $184.512   $184.51   $184.50   $184.50  
  Purchase #6 $119.92   5.210%   $126.1678   $126.17   $126.15   $126.20  
  Purchase #7 $249.48   10.637%   $276.0172   $276.02   $276.00   $276.00  
  7 purchase totals = $1,012.98       $1,098.0096   $1,098.01   $1,098.00   $1,098.00