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 $63.29   8.514%   $68.6785   $68.68   $68.70   $68.70  
  Purchase #2 $37.49   6.388%   $39.8849   $39.88   $39.90   $39.90  
  Purchase #3 $240.73   10.153%   $265.1713   $265.17   $265.15   $265.20  
  Purchase #4 $55.44   12.711%   $62.487   $62.49   $62.50   $62.50  
  Purchase #5 $100.40   9.286%   $109.7231   $109.72   $109.70   $109.70  
  Purchase #6 $120.90   7.104%   $129.4887   $129.49   $129.50   $129.50  
  Purchase #7 $44.92   10.421%   $49.6011   $49.60   $49.60   $49.60  
  7 purchase totals = $663.17       $725.0346   $725.03   $725.05   $725.10