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 $57.92   6.494%   $61.6813   $61.68   $61.70   $61.70  
  Purchase #2 $179.93   11.512%   $200.6435   $200.64   $200.65   $200.60  
  Purchase #3 $78.86   4.184%   $82.1595   $82.16   $82.15   $82.20  
  Purchase #4 $242.48   9.388%   $265.244   $265.24   $265.25   $265.20  
  Purchase #5 $244.27   3.607%   $253.0808   $253.08   $253.10   $253.10  
  Purchase #6 $242.83   7.765%   $261.6857   $261.69   $261.70   $261.70  
  Purchase #7 $61.85   13.511%   $70.2066   $70.21   $70.20   $70.20  
  7 purchase totals = $1,108.14       $1,194.7014   $1,194.70   $1,194.75   $1,194.70