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 $169.88   10.117%   $187.0668   $187.07   $187.05   $187.10  
  Purchase #2 $127.80   8.741%   $138.971   $138.97   $138.95   $139.00  
  Purchase #3 $163.43   5.243%   $171.9986   $172.00   $172.00   $172.00  
  Purchase #4 $9.30   9.600%   $10.1928   $10.19   $10.20   $10.20  
  Purchase #5 $11.37   11.497%   $12.6772   $12.68   $12.70   $12.70  
  Purchase #6 $99.86   5.565%   $105.4172   $105.42   $105.40   $105.40  
  Purchase #7 $79.32   13.200%   $89.7902   $89.79   $89.80   $89.80  
  7 purchase totals = $660.96       $716.1138   $716.12   $716.10   $716.20