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 $110.67   9.273%   $120.9324   $120.93   $120.95   $120.90  
  Purchase #2 $152.32   4.566%   $159.2749   $159.27   $159.25   $159.30  
  Purchase #3 $44.25   4.482%   $46.2333   $46.23   $46.25   $46.20  
  Purchase #4 $55.83   10.873%   $61.9004   $61.90   $61.90   $61.90  
  Purchase #5 $114.86   9.563%   $125.8441   $125.84   $125.85   $125.80  
  Purchase #6 $194.83   7.532%   $209.5046   $209.50   $209.50   $209.50  
  Purchase #7 $22.53   6.485%   $23.9911   $23.99   $24.00   $24.00  
  7 purchase totals = $695.29       $747.6808   $747.66   $747.70   $747.60