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 $120.61   5.564%   $127.3207   $127.32   $127.30   $127.30  
  Purchase #2 $18.25   10.548%   $20.175   $20.18   $20.20   $20.20  
  Purchase #3 $49.65   7.639%   $53.4428   $53.44   $53.45   $53.40  
  Purchase #4 $179.26   13.671%   $203.7666   $203.77   $203.75   $203.80  
  Purchase #5 $67.97   8.222%   $73.5585   $73.56   $73.55   $73.60  
  Purchase #6 $132.62   11.655%   $148.0769   $148.08   $148.10   $148.10  
  Purchase #7 $196.39   6.846%   $209.8349   $209.83   $209.85   $209.80  
  7 purchase totals = $764.75       $836.1754   $836.18   $836.20   $836.20