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 $250.75   8.460%   $271.9635   $271.96   $271.95   $272.00  
  Purchase #2 $203.95   10.569%   $225.5055   $225.51   $225.50   $225.50  
  Purchase #3 $236.48   13.402%   $268.173   $268.17   $268.15   $268.20  
  Purchase #4 $206.62   5.254%   $217.4758   $217.48   $217.50   $217.50  
  Purchase #5 $16.30   3.773%   $16.915   $16.92   $16.90   $16.90  
  Purchase #6 $189.52   12.140%   $212.5277   $212.53   $212.55   $212.50  
  Purchase #7 $14.48   3.491%   $14.9855   $14.99   $15.00   $15.00  
  7 purchase totals = $1,118.10       $1,227.5460   $1,227.56   $1,227.55   $1,227.60