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 $92.33   6.393%   $98.2327   $98.23   $98.25   $98.20  
  Purchase #2 $219.50   8.721%   $238.6426   $238.64   $238.65   $238.60  
  Purchase #3 $235.99   4.256%   $246.0337   $246.03   $246.05   $246.00  
  Purchase #4 $13.38   3.690%   $13.8737   $13.87   $13.85   $13.90  
  Purchase #5 $83.37   6.824%   $89.0592   $89.06   $89.05   $89.10  
  Purchase #6 $12.58   5.732%   $13.3011   $13.30   $13.30   $13.30  
  Purchase #7 $235.90   7.619%   $253.8732   $253.87   $253.85   $253.90  
  7 purchase totals = $893.05       $953.0162   $953.00   $953.00   $953.00