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 $84.87   11.817%   $94.8991   $94.90   $94.90   $94.90  
  Purchase #2 $55.44   8.181%   $59.9755   $59.98   $60.00   $60.00  
  Purchase #3 $220.58   5.782%   $233.3339   $233.33   $233.35   $233.30  
  Purchase #4 $22.71   6.381%   $24.1591   $24.16   $24.15   $24.20  
  Purchase #5 $165.73   13.594%   $188.2593   $188.26   $188.25   $188.30  
  Purchase #6 $109.54   11.114%   $121.7143   $121.71   $121.70   $121.70  
  Purchase #7 $141.45   7.211%   $151.65   $151.65   $151.65   $151.70  
  7 purchase totals = $800.32       $873.9912   $873.99   $874.00   $874.10