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 $246.45   6.404%   $262.2327   $262.23   $262.25   $262.20  
  Purchase #2 $32.81   12.591%   $36.9411   $36.94   $36.95   $36.90  
  Purchase #3 $107.32   9.850%   $117.891   $117.89   $117.90   $117.90  
  Purchase #4 $155.51   11.434%   $173.291   $173.29   $173.30   $173.30  
  Purchase #5 $207.93   9.417%   $227.5108   $227.51   $227.50   $227.50  
  Purchase #6 $242.51   9.795%   $266.2639   $266.26   $266.25   $266.30  
  Purchase #7 $112.96   9.470%   $123.6573   $123.66   $123.65   $123.70  
  7 purchase totals = $1,105.49       $1,207.7878   $1,207.78   $1,207.80   $1,207.80