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 $98.81   12.218%   $110.8826   $110.88   $110.90   $110.90  
  Purchase #2 $238.93   9.511%   $261.6546   $261.65   $261.65   $261.70  
  Purchase #3 $123.36   5.541%   $130.1954   $130.20   $130.20   $130.20  
  Purchase #4 $123.92   10.852%   $137.3678   $137.37   $137.35   $137.40  
  Purchase #5 $62.39   4.112%   $64.9555   $64.96   $64.95   $65.00  
  Purchase #6 $184.44   10.126%   $203.1164   $203.12   $203.10   $203.10  
  Purchase #7 $61.99   3.456%   $64.1324   $64.13   $64.15   $64.10  
  7 purchase totals = $893.84       $972.3047   $972.31   $972.30   $972.40