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 $212.61   8.185%   $230.0121   $230.01   $230.00   $230.00  
  Purchase #2 $199.61   11.231%   $222.0282   $222.03   $222.05   $222.00  
  Purchase #3 $33.55   8.494%   $36.3997   $36.40   $36.40   $36.40  
  Purchase #4 $61.63   4.865%   $64.6283   $64.63   $64.65   $64.60  
  Purchase #5 $7.68   6.123%   $8.1502   $8.15   $8.15   $8.20  
  Purchase #6 $167.66   8.118%   $181.2706   $181.27   $181.25   $181.30  
  Purchase #7 $212.49   4.359%   $221.7524   $221.75   $221.75   $221.80  
  7 purchase totals = $895.23       $964.2415   $964.24   $964.25   $964.30