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 $195.62   7.351%   $210   $210.00   $210.00   $210.00  
  Purchase #2 $180.91   7.143%   $193.8324   $193.83   $193.85   $193.80  
  Purchase #3 $161.38   3.253%   $166.6297   $166.63   $166.65   $166.60  
  Purchase #4 $34.36   7.841%   $37.0542   $37.05   $37.05   $37.10  
  Purchase #5 $207.38   13.108%   $234.5634   $234.56   $234.55   $234.60  
  Purchase #6 $54.77   13.218%   $62.0095   $62.01   $62.00   $62.00  
  Purchase #7 $119.48   4.588%   $124.9617   $124.96   $124.95   $125.00  
  7 purchase totals = $953.90       $1,029.0509   $1,029.04   $1,029.05   $1,029.10