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 $88.98   6.199%   $94.4959   $94.50   $94.50   $94.50  
  Purchase #2 $218.42   13.857%   $248.6865   $248.69   $248.70   $248.70  
  Purchase #3 $98.81   11.846%   $110.515   $110.52   $110.50   $110.50  
  Purchase #4 $154.70   6.846%   $165.2908   $165.29   $165.30   $165.30  
  Purchase #5 $168.99   6.664%   $180.2515   $180.25   $180.25   $180.30  
  Purchase #6 $242.63   6.305%   $257.9278   $257.93   $257.95   $257.90  
  Purchase #7 $86.45   3.229%   $89.2415   $89.24   $89.25   $89.20  
  7 purchase totals = $1,058.98       $1,146.4090   $1,146.42   $1,146.45   $1,146.40