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 $61.54   10.753%   $68.1574   $68.16   $68.15   $68.20  
  Purchase #2 $81.64   4.482%   $85.2991   $85.30   $85.30   $85.30  
  Purchase #3 $152.93   8.124%   $165.354   $165.35   $165.35   $165.40  
  Purchase #4 $221.65   13.361%   $251.2647   $251.26   $251.25   $251.30  
  Purchase #5 $94.33   8.420%   $102.2726   $102.27   $102.25   $102.30  
  Purchase #6 $19.42   9.765%   $21.3164   $21.32   $21.30   $21.30  
  Purchase #7 $144.27   10.647%   $159.6304   $159.63   $159.65   $159.60  
  7 purchase totals = $775.78       $853.2946   $853.29   $853.25   $853.40