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 $34.87   7.758%   $37.5752   $37.58   $37.60   $37.60  
  Purchase #2 $16.58   4.267%   $17.2875   $17.29   $17.30   $17.30  
  Purchase #3 $69.85   13.690%   $79.4125   $79.41   $79.40   $79.40  
  Purchase #4 $243.91   3.144%   $251.5785   $251.58   $251.60   $251.60  
  Purchase #5 $40.40   5.684%   $42.6963   $42.70   $42.70   $42.70  
  Purchase #6 $141.81   12.317%   $159.2767   $159.28   $159.30   $159.30  
  Purchase #7 $173.93   13.357%   $197.1618   $197.16   $197.15   $197.20  
  7 purchase totals = $721.35       $784.9885   $785.00   $785.05   $785.10