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 $88.57   4.648%   $92.6867   $92.69   $92.70   $92.70  
  Purchase #2 $63.25   5.285%   $66.5928   $66.59   $66.60   $66.60  
  Purchase #3 $63.91   5.367%   $67.34   $67.34   $67.35   $67.30  
  Purchase #4 $60.96   9.361%   $66.6665   $66.67   $66.65   $66.70  
  Purchase #5 $205.40   11.785%   $229.6064   $229.61   $229.60   $229.60  
  Purchase #6 $55.47   5.708%   $58.6362   $58.64   $58.65   $58.60  
  Purchase #7 $46.25   8.152%   $50.0203   $50.02   $50.00   $50.00  
  7 purchase totals = $583.81       $631.5489   $631.56   $631.55   $631.50