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 $108.69   13.661%   $123.5381   $123.54   $123.55   $123.50  
  Purchase #2 $240.58   7.257%   $258.0389   $258.04   $258.05   $258.00  
  Purchase #3 $206.80   5.721%   $218.631   $218.63   $218.65   $218.60  
  Purchase #4 $231.96   12.229%   $260.3264   $260.33   $260.35   $260.30  
  Purchase #5 $244.50   10.290%   $269.6591   $269.66   $269.65   $269.70  
  Purchase #6 $119.61   13.497%   $135.7538   $135.75   $135.75   $135.80  
  Purchase #7 $225.80   3.541%   $233.7956   $233.80   $233.80   $233.80  
  7 purchase totals = $1,377.94       $1,499.7429   $1,499.75   $1,499.80   $1,499.70