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 $90.87   5.711%   $96.0596   $96.06   $96.05   $96.10  
  Purchase #2 $130.85   13.797%   $148.9034   $148.90   $148.90   $148.90  
  Purchase #3 $170.26   8.688%   $185.0522   $185.05   $185.05   $185.10  
  Purchase #4 $58.73   5.628%   $62.0353   $62.04   $62.05   $62.00  
  Purchase #5 $76.52   13.108%   $86.5502   $86.55   $86.55   $86.60  
  Purchase #6 $173.97   3.163%   $179.4727   $179.47   $179.45   $179.50  
  Purchase #7 $187.70   12.221%   $210.6388   $210.64   $210.65   $210.60  
  7 purchase totals = $888.90       $968.7122   $968.71   $968.70   $968.80