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 $246.37   11.244%   $274.0718   $274.07   $274.05   $274.10  
  Purchase #2 $63.74   3.500%   $65.9709   $65.97   $65.95   $66.00  
  Purchase #3 $63.58   5.620%   $67.1532   $67.15   $67.15   $67.20  
  Purchase #4 $201.94   3.177%   $208.3556   $208.36   $208.35   $208.40  
  Purchase #5 $239.53   6.397%   $254.8527   $254.85   $254.85   $254.90  
  Purchase #6 $223.86   6.742%   $238.9526   $238.95   $238.95   $239.00  
  Purchase #7 $13.50   3.657%   $13.9937   $13.99   $14.00   $14.00  
  7 purchase totals = $1,052.52       $1,123.3505   $1,123.34   $1,123.30   $1,123.60