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 $84.25   11.165%   $93.6565   $93.66   $93.65   $93.70  
  Purchase #2 $68.95   4.495%   $72.0493   $72.05   $72.05   $72.00  
  Purchase #3 $195.33   9.812%   $214.4958   $214.50   $214.50   $214.50  
  Purchase #4 $66.59   8.487%   $72.2415   $72.24   $72.25   $72.20  
  Purchase #5 $109.80   13.498%   $124.6208   $124.62   $124.60   $124.60  
  Purchase #6 $68.85   6.470%   $73.3046   $73.30   $73.30   $73.30  
  Purchase #7 $220.60   6.545%   $235.0383   $235.04   $235.05   $235.00  
  7 purchase totals = $814.37       $885.4068   $885.41   $885.40   $885.30