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 $55.95   9.293%   $61.1494   $61.15   $61.15   $61.10  
  Purchase #2 $205.58   6.359%   $218.6528   $218.65   $218.65   $218.70  
  Purchase #3 $43.49   5.566%   $45.9107   $45.91   $45.90   $45.90  
  Purchase #4 $88.62   9.165%   $96.742   $96.74   $96.75   $96.70  
  Purchase #5 $139.54   9.585%   $152.9149   $152.91   $152.90   $152.90  
  Purchase #6 $228.26   11.405%   $254.2931   $254.29   $254.30   $254.30  
  Purchase #7 $64.94   6.403%   $69.0981   $69.10   $69.10   $69.10  
  7 purchase totals = $826.38       $898.7610   $898.75   $898.75   $898.70