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 $83.41   13.151%   $94.3792   $94.38   $94.40   $94.40  
  Purchase #2 $98.57   9.226%   $107.6641   $107.66   $107.65   $107.70  
  Purchase #3 $63.48   11.544%   $70.8081   $70.81   $70.80   $70.80  
  Purchase #4 $163.36   4.659%   $170.9709   $170.97   $170.95   $171.00  
  Purchase #5 $27.80   6.643%   $29.6468   $29.65   $29.65   $29.60  
  Purchase #6 $103.70   4.812%   $108.69   $108.69   $108.70   $108.70  
  Purchase #7 $144.63   7.516%   $155.5004   $155.50   $155.50   $155.50  
  7 purchase totals = $684.95       $737.6595   $737.66   $737.65   $737.70