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 $104.68   8.462%   $113.538   $113.54   $113.55   $113.50  
  Purchase #2 $14.38   8.872%   $15.6558   $15.66   $15.65   $15.70  
  Purchase #3 $178.93   12.674%   $201.6076   $201.61   $201.60   $201.60  
  Purchase #4 $119.68   8.720%   $130.1161   $130.12   $130.10   $130.10  
  Purchase #5 $142.84   11.316%   $159.0038   $159.00   $159.00   $159.00  
  Purchase #6 $200.44   7.171%   $214.8136   $214.81   $214.80   $214.80  
  Purchase #7 $233.49   12.647%   $263.0195   $263.02   $263.00   $263.00  
  7 purchase totals = $994.44       $1,097.7544   $1,097.76   $1,097.70   $1,097.70