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 $99.49   8.371%   $107.8183   $107.82   $107.80   $107.80  
  Purchase #2 $159.36   9.147%   $173.9367   $173.94   $173.95   $173.90  
  Purchase #3 $8.58   13.471%   $9.7358   $9.74   $9.75   $9.70  
  Purchase #4 $50.37   5.185%   $52.9817   $52.98   $53.00   $53.00  
  Purchase #5 $221.93   3.277%   $229.2026   $229.20   $229.20   $229.20  
  Purchase #6 $188.75   3.806%   $195.9338   $195.93   $195.95   $195.90  
  Purchase #7 $114.46   9.545%   $125.3852   $125.39   $125.40   $125.40  
  7 purchase totals = $842.94       $894.9941   $895.00   $895.05   $894.90