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 $152.96   8.657%   $166.2017   $166.20   $166.20   $166.20  
  Purchase #2 $132.65   13.373%   $150.3893   $150.39   $150.40   $150.40  
  Purchase #3 $182.38   9.289%   $199.3213   $199.32   $199.30   $199.30  
  Purchase #4 $70.49   7.855%   $76.027   $76.03   $76.05   $76.00  
  Purchase #5 $30.49   7.868%   $32.889   $32.89   $32.90   $32.90  
  Purchase #6 $145.83   10.393%   $160.9861   $160.99   $161.00   $161.00  
  Purchase #7 $20.82   6.585%   $22.191   $22.19   $22.20   $22.20  
  7 purchase totals = $735.62       $808.0054   $808.01   $808.05   $808.00