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 $93.85   11.152%   $104.3162   $104.32   $104.30   $104.30  
  Purchase #2 $181.92   8.287%   $196.9957   $197.00   $197.00   $197.00  
  Purchase #3 $63.89   10.552%   $70.6317   $70.63   $70.65   $70.60  
  Purchase #4 $191.98   6.102%   $203.6946   $203.69   $203.70   $203.70  
  Purchase #5 $25.46   10.174%   $28.0503   $28.05   $28.05   $28.10  
  Purchase #6 $78.53   6.492%   $83.6282   $83.63   $83.65   $83.60  
  Purchase #7 $74.73   7.193%   $80.1053   $80.11   $80.10   $80.10  
  7 purchase totals = $710.36       $767.4220   $767.43   $767.45   $767.40