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 $195.74   10.498%   $216.2888   $216.29   $216.30   $216.30  
  Purchase #2 $116.55   8.641%   $126.6211   $126.62   $126.60   $126.60  
  Purchase #3 $209.89   6.371%   $223.2621   $223.26   $223.25   $223.30  
  Purchase #4 $31.25   3.766%   $32.4269   $32.43   $32.45   $32.40  
  Purchase #5 $46.48   6.671%   $49.5807   $49.58   $49.60   $49.60  
  Purchase #6 $189.96   11.526%   $211.8548   $211.85   $211.85   $211.90  
  Purchase #7 $79.26   6.664%   $84.5419   $84.54   $84.55   $84.50  
  7 purchase totals = $869.13       $944.5763   $944.57   $944.60   $944.60