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 $32.82   8.279%   $35.5372   $35.54   $35.55   $35.50  
  Purchase #2 $33.87   11.159%   $37.6496   $37.65   $37.65   $37.60  
  Purchase #3 $94.91   4.666%   $99.3385   $99.34   $99.35   $99.30  
  Purchase #4 $44.25   11.261%   $49.233   $49.23   $49.25   $49.20  
  Purchase #5 $241.77   4.128%   $251.7503   $251.75   $251.75   $251.80  
  Purchase #6 $147.41   12.197%   $165.3896   $165.39   $165.40   $165.40  
  Purchase #7 $21.41   11.171%   $23.8017   $23.80   $23.80   $23.80  
  7 purchase totals = $616.44       $662.6999   $662.70   $662.75   $662.60