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 $81.95   3.331%   $84.6798   $84.68   $84.70   $84.70  
  Purchase #2 $208.77   3.561%   $216.2043   $216.20   $216.20   $216.20  
  Purchase #3 $126.48   10.555%   $139.83   $139.83   $139.85   $139.80  
  Purchase #4 $112.54   12.705%   $126.8382   $126.84   $126.85   $126.80  
  Purchase #5 $240.48   12.119%   $269.6238   $269.62   $269.60   $269.60  
  Purchase #6 $140.38   13.248%   $158.9775   $158.98   $159.00   $159.00  
  Purchase #7 $108.78   13.422%   $123.3805   $123.38   $123.40   $123.40  
  7 purchase totals = $1,019.38       $1,119.5341   $1,119.53   $1,119.60   $1,119.50