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 $173.92   11.457%   $193.846   $193.85   $193.85   $193.80  
  Purchase #2 $232.90   10.729%   $257.8878   $257.89   $257.90   $257.90  
  Purchase #3 $234.56   4.511%   $245.141   $245.14   $245.15   $245.10  
  Purchase #4 $249.25   3.254%   $257.3606   $257.36   $257.35   $257.40  
  Purchase #5 $135.67   4.138%   $141.284   $141.28   $141.30   $141.30  
  Purchase #6 $78.35   8.492%   $85.0035   $85.00   $85.00   $85.00  
  Purchase #7 $231.75   11.411%   $258.195   $258.20   $258.20   $258.20  
  7 purchase totals = $1,336.40       $1,438.7179   $1,438.72   $1,438.75   $1,438.70