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 $66.70   4.181%   $69.4887   $69.49   $69.50   $69.50  
  Purchase #2 $181.90   10.480%   $200.9631   $200.96   $200.95   $201.00  
  Purchase #3 $156.70   7.279%   $168.1062   $168.11   $168.10   $168.10  
  Purchase #4 $204.93   7.126%   $219.5333   $219.53   $219.55   $219.50  
  Purchase #5 $72.48   5.468%   $76.4432   $76.44   $76.45   $76.40  
  Purchase #6 $187.60   11.865%   $209.8587   $209.86   $209.85   $209.90  
  Purchase #7 $109.45   6.210%   $116.2468   $116.25   $116.25   $116.20  
  7 purchase totals = $979.76       $1,060.6400   $1,060.64   $1,060.65   $1,060.60