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 $118.82   7.372%   $127.5794   $127.58   $127.60   $127.60  
  Purchase #2 $58.30   4.143%   $60.7154   $60.72   $60.70   $60.70  
  Purchase #3 $39.42   3.138%   $40.657   $40.66   $40.65   $40.70  
  Purchase #4 $211.71   9.652%   $232.1442   $232.14   $232.15   $232.10  
  Purchase #5 $164.53   4.330%   $171.6541   $171.65   $171.65   $171.70  
  Purchase #6 $74.99   9.172%   $81.8681   $81.87   $81.85   $81.90  
  Purchase #7 $37.56   5.331%   $39.5623   $39.56   $39.55   $39.60  
  7 purchase totals = $705.33       $754.1805   $754.18   $754.15   $754.30