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 $167.86   6.769%   $179.2224   $179.22   $179.20   $179.20  
  Purchase #2 $63.93   5.734%   $67.5957   $67.60   $67.60   $67.60  
  Purchase #3 $95.33   7.152%   $102.148   $102.15   $102.15   $102.10  
  Purchase #4 $59.41   6.541%   $63.296   $63.30   $63.30   $63.30  
  Purchase #5 $105.63   4.133%   $109.9957   $110.00   $110.00   $110.00  
  Purchase #6 $140.31   13.220%   $158.859   $158.86   $158.85   $158.90  
  Purchase #7 $48.96   4.156%   $50.9948   $50.99   $51.00   $51.00  
  7 purchase totals = $681.43       $732.1116   $732.12   $732.10   $732.10