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 $219.53   11.561%   $244.9099   $244.91   $244.90   $244.90  
  Purchase #2 $184.32   10.368%   $203.4303   $203.43   $203.45   $203.40  
  Purchase #3 $180.83   4.263%   $188.5388   $188.54   $188.55   $188.50  
  Purchase #4 $64.97   7.448%   $69.809   $69.81   $69.80   $69.80  
  Purchase #5 $35.97   6.425%   $38.2811   $38.28   $38.30   $38.30  
  Purchase #6 $15.94   6.263%   $16.9383   $16.94   $16.95   $16.90  
  Purchase #7 $95.96   12.818%   $108.2602   $108.26   $108.25   $108.30  
  7 purchase totals = $797.52       $870.1676   $870.17   $870.20   $870.10