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 $172.31   13.265%   $195.1669   $195.17   $195.15   $195.20  
  Purchase #2 $153.57   3.650%   $159.1753   $159.18   $159.20   $159.20  
  Purchase #3 $239.29   5.394%   $252.1973   $252.20   $252.20   $252.20  
  Purchase #4 $55.68   4.251%   $58.047   $58.05   $58.05   $58.00  
  Purchase #5 $169.87   10.674%   $188.0019   $188.00   $188.00   $188.00  
  Purchase #6 $60.98   6.347%   $64.8504   $64.85   $64.85   $64.90  
  Purchase #7 $69.72   9.871%   $76.6021   $76.60   $76.60   $76.60  
  7 purchase totals = $921.42       $994.0409   $994.05   $994.05   $994.10