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 $65.56   8.579%   $71.1844   $71.18   $71.20   $71.20  
  Purchase #2 $236.55   4.649%   $247.5472   $247.55   $247.55   $247.50  
  Purchase #3 $16.85   12.461%   $18.9497   $18.95   $18.95   $18.90  
  Purchase #4 $148.26   9.194%   $161.891   $161.89   $161.90   $161.90  
  Purchase #5 $227.53   8.329%   $246.481   $246.48   $246.50   $246.50  
  Purchase #6 $62.26   12.441%   $70.0058   $70.01   $70.00   $70.00  
  Purchase #7 $244.40   3.494%   $252.9393   $252.94   $252.95   $252.90  
  7 purchase totals = $1,001.41       $1,068.9984   $1,069.00   $1,069.05   $1,068.90