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 $86.74   8.418%   $94.0418   $94.04   $94.05   $94.00  
  Purchase #2 $157.66   10.854%   $174.7724   $174.77   $174.75   $174.80  
  Purchase #3 $167.42   4.791%   $175.4411   $175.44   $175.45   $175.40  
  Purchase #4 $11.88   8.713%   $12.9151   $12.92   $12.90   $12.90  
  Purchase #5 $6.31   9.370%   $6.9012   $6.90   $6.90   $6.90  
  Purchase #6 $26.75   8.375%   $28.9903   $28.99   $29.00   $29.00  
  Purchase #7 $246.62   3.768%   $255.9126   $255.91   $255.90   $255.90  
  7 purchase totals = $703.38       $748.9745   $748.97   $748.95   $748.90