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 $63.81   6.759%   $68.1229   $68.12   $68.10   $68.10  
  Purchase #2 $159.95   13.763%   $181.9639   $181.96   $181.95   $182.00  
  Purchase #3 $213.95   8.378%   $231.8747   $231.87   $231.85   $231.90  
  Purchase #4 $116.45   7.765%   $125.4923   $125.49   $125.50   $125.50  
  Purchase #5 $232.67   10.823%   $257.8519   $257.85   $257.85   $257.90  
  Purchase #6 $234.76   7.820%   $253.1182   $253.12   $253.10   $253.10  
  Purchase #7 $61.87   3.490%   $64.0293   $64.03   $64.05   $64.00  
  7 purchase totals = $1,083.46       $1,182.4532   $1,182.44   $1,182.40   $1,182.50