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 $243.56   6.472%   $259.3232   $259.32   $259.30   $259.30  
  Purchase #2 $130.27   4.706%   $136.4005   $136.40   $136.40   $136.40  
  Purchase #3 $221.90   9.601%   $243.2046   $243.20   $243.20   $243.20  
  Purchase #4 $57.80   4.802%   $60.5756   $60.58   $60.60   $60.60  
  Purchase #5 $183.92   5.518%   $194.0687   $194.07   $194.05   $194.10  
  Purchase #6 $239.94   12.313%   $269.4838   $269.48   $269.50   $269.50  
  Purchase #7 $250.50   5.620%   $264.5781   $264.58   $264.60   $264.60  
  7 purchase totals = $1,327.89       $1,427.6345   $1,427.63   $1,427.65   $1,427.70