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 $110.68   7.760%   $119.2688   $119.27   $119.25   $119.30  
  Purchase #2 $212.75   6.216%   $225.9745   $225.97   $225.95   $226.00  
  Purchase #3 $83.61   11.466%   $93.1967   $93.20   $93.20   $93.20  
  Purchase #4 $32.32   11.792%   $36.1312   $36.13   $36.15   $36.10  
  Purchase #5 $98.81   12.430%   $111.0921   $111.09   $111.10   $111.10  
  Purchase #6 $64.63   12.436%   $72.6674   $72.67   $72.65   $72.70  
  Purchase #7 $160.77   10.495%   $177.6428   $177.64   $177.65   $177.60  
  7 purchase totals = $763.57       $835.9735   $835.97   $835.95   $836.00