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 $41.67   4.624%   $43.5968   $43.60   $43.60   $43.60  
  Purchase #2 $117.62   10.146%   $129.5537   $129.55   $129.55   $129.60  
  Purchase #3 $130.33   9.461%   $142.6605   $142.66   $142.65   $142.70  
  Purchase #4 $136.84   12.205%   $153.5413   $153.54   $153.55   $153.50  
  Purchase #5 $55.85   9.678%   $61.2552   $61.26   $61.25   $61.30  
  Purchase #6 $84.75   12.387%   $95.248   $95.25   $95.25   $95.20  
  Purchase #7 $107.76   7.319%   $115.647   $115.65   $115.65   $115.60  
  7 purchase totals = $674.82       $741.5025   $741.51   $741.50   $741.50