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 $193.70   8.267%   $209.7132   $209.71   $209.70   $209.70  
  Purchase #2 $84.64   11.801%   $94.6284   $94.63   $94.65   $94.60  
  Purchase #3 $215.27   13.497%   $244.325   $244.33   $244.35   $244.30  
  Purchase #4 $135.62   4.810%   $142.1433   $142.14   $142.15   $142.10  
  Purchase #5 $68.70   11.865%   $76.8513   $76.85   $76.85   $76.90  
  Purchase #6 $106.44   4.445%   $111.1713   $111.17   $111.15   $111.20  
  Purchase #7 $170.76   6.458%   $181.7877   $181.79   $181.80   $181.80  
  7 purchase totals = $975.13       $1,060.6202   $1,060.62   $1,060.65   $1,060.60