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 $22.76   9.531%   $24.9293   $24.93   $24.95   $24.90  
  Purchase #2 $77.37   10.701%   $85.6494   $85.65   $85.65   $85.60  
  Purchase #3 $67.55   8.231%   $73.11   $73.11   $73.10   $73.10  
  Purchase #4 $191.28   7.543%   $205.7083   $205.71   $205.70   $205.70  
  Purchase #5 $212.92   10.501%   $235.2787   $235.28   $235.30   $235.30  
  Purchase #6 $122.31   8.535%   $132.7492   $132.75   $132.75   $132.70  
  Purchase #7 $127.46   7.327%   $136.799   $136.80   $136.80   $136.80  
  7 purchase totals = $821.65       $894.2239   $894.23   $894.25   $894.10