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 $49.46   6.619%   $52.7338   $52.73   $52.75   $52.70  
  Purchase #2 $100.43   9.729%   $110.2008   $110.20   $110.20   $110.20  
  Purchase #3 $235.86   10.867%   $261.4909   $261.49   $261.50   $261.50  
  Purchase #4 $151.67   3.274%   $156.6357   $156.64   $156.65   $156.60  
  Purchase #5 $181.58   13.489%   $206.0733   $206.07   $206.05   $206.10  
  Purchase #6 $116.52   11.688%   $130.1389   $130.14   $130.15   $130.10  
  Purchase #7 $226.80   9.439%   $248.2077   $248.21   $248.20   $248.20  
  7 purchase totals = $1,062.32       $1,165.4811   $1,165.48   $1,165.50   $1,165.40