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 $178.42   13.691%   $202.8475   $202.85   $202.85   $202.80  
  Purchase #2 $34.92   4.180%   $36.3797   $36.38   $36.40   $36.40  
  Purchase #3 $14.94   13.220%   $16.9151   $16.92   $16.90   $16.90  
  Purchase #4 $196.26   5.240%   $206.544   $206.54   $206.55   $206.50  
  Purchase #5 $233.84   3.226%   $241.3837   $241.38   $241.40   $241.40  
  Purchase #6 $68.67   3.397%   $71.0027   $71.00   $71.00   $71.00  
  Purchase #7 $96.50   5.611%   $101.9146   $101.91   $101.90   $101.90  
  7 purchase totals = $823.55       $876.9873   $876.98   $877.00   $876.90