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 $24.77   6.226%   $26.3122   $26.31   $26.30   $26.30  
  Purchase #2 $232.30   11.687%   $259.4489   $259.45   $259.45   $259.40  
  Purchase #3 $111.35   5.732%   $117.7326   $117.73   $117.75   $117.70  
  Purchase #4 $188.36   10.277%   $207.7178   $207.72   $207.70   $207.70  
  Purchase #5 $160.65   10.140%   $176.9399   $176.94   $176.95   $176.90  
  Purchase #6 $23.74   11.498%   $26.4696   $26.47   $26.45   $26.50  
  Purchase #7 $185.31   7.655%   $199.4955   $199.50   $199.50   $199.50  
  7 purchase totals = $926.48       $1,014.1165   $1,014.12   $1,014.10   $1,014.00