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 $62.72   7.158%   $67.2095   $67.21   $67.20   $67.20  
  Purchase #2 $82.84   7.166%   $88.7763   $88.78   $88.80   $88.80  
  Purchase #3 $200.30   7.253%   $214.8278   $214.83   $214.85   $214.80  
  Purchase #4 $245.87   8.581%   $266.9681   $266.97   $266.95   $267.00  
  Purchase #5 $124.75   10.820%   $138.248   $138.25   $138.25   $138.20  
  Purchase #6 $192.91   10.693%   $213.5379   $213.54   $213.55   $213.50  
  Purchase #7 $173.57   12.583%   $195.4103   $195.41   $195.40   $195.40  
  7 purchase totals = $1,082.96       $1,184.9779   $1,184.99   $1,185.00   $1,184.90