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 $46.78   4.752%   $49.003   $49.00   $49.00   $49.00  
  Purchase #2 $51.79   9.505%   $56.7126   $56.71   $56.70   $56.70  
  Purchase #3 $35.51   3.477%   $36.7447   $36.74   $36.75   $36.70  
  Purchase #4 $249.67   7.275%   $267.8335   $267.83   $267.85   $267.80  
  Purchase #5 $154.72   8.485%   $167.848   $167.85   $167.85   $167.80  
  Purchase #6 $104.93   11.801%   $117.3128   $117.31   $117.30   $117.30  
  Purchase #7 $120.26   12.524%   $135.3214   $135.32   $135.30   $135.30  
  7 purchase totals = $763.66       $830.7760   $830.76   $830.75   $830.60