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 $100.25   6.728%   $106.9948   $106.99   $107.00   $107.00  
  Purchase #2 $127.89   9.864%   $140.5051   $140.51   $140.50   $140.50  
  Purchase #3 $30.26   3.741%   $31.392   $31.39   $31.40   $31.40  
  Purchase #4 $183.30   12.612%   $206.4178   $206.42   $206.40   $206.40  
  Purchase #5 $10.49   3.779%   $10.8864   $10.89   $10.90   $10.90  
  Purchase #6 $121.98   13.866%   $138.8937   $138.89   $138.90   $138.90  
  Purchase #7 $104.80   12.370%   $117.7638   $117.76   $117.75   $117.80  
  7 purchase totals = $678.97       $752.8536   $752.85   $752.85   $752.90