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 $75.41   12.726%   $85.0067   $85.01   $85.00   $85.00  
  Purchase #2 $117.84   5.664%   $124.5145   $124.51   $124.50   $124.50  
  Purchase #3 $166.31   5.788%   $175.936   $175.94   $175.95   $175.90  
  Purchase #4 $128.92   6.210%   $136.9259   $136.93   $136.95   $136.90  
  Purchase #5 $56.86   12.357%   $63.8862   $63.89   $63.90   $63.90  
  Purchase #6 $172.73   13.217%   $195.5597   $195.56   $195.55   $195.60  
  Purchase #7 $223.56   8.453%   $242.4575   $242.46   $242.45   $242.50  
  7 purchase totals = $941.63       $1,024.2865   $1,024.30   $1,024.30   $1,024.30