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 $23.56   5.836%   $24.935   $24.94   $24.95   $24.90  
  Purchase #2 $194.44   5.218%   $204.5859   $204.59   $204.60   $204.60  
  Purchase #3 $58.64   4.341%   $61.1856   $61.19   $61.20   $61.20  
  Purchase #4 $130.44   10.469%   $144.0958   $144.10   $144.10   $144.10  
  Purchase #5 $13.91   6.178%   $14.7694   $14.77   $14.75   $14.80  
  Purchase #6 $49.69   4.416%   $51.8843   $51.88   $51.90   $51.90  
  Purchase #7 $96.39   4.825%   $101.0408   $101.04   $101.05   $101.00  
  7 purchase totals = $567.07       $602.4968   $602.51   $602.55   $602.50