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 $88.80   5.474%   $93.6609   $93.66   $93.65   $93.70  
  Purchase #2 $151.64   6.610%   $161.6634   $161.66   $161.65   $161.70  
  Purchase #3 $194.87   12.145%   $218.537   $218.54   $218.55   $218.50  
  Purchase #4 $113.64   6.200%   $120.6857   $120.69   $120.70   $120.70  
  Purchase #5 $78.81   5.305%   $82.9909   $82.99   $83.00   $83.00  
  Purchase #6 $220.80   7.357%   $237.0443   $237.04   $237.05   $237.00  
  Purchase #7 $64.71   12.726%   $72.945   $72.95   $72.95   $72.90  
  7 purchase totals = $913.27       $987.5272   $987.53   $987.55   $987.50