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 $91.80   13.546%   $104.2352   $104.24   $104.25   $104.20  
  Purchase #2 $159.50   3.199%   $164.6024   $164.60   $164.60   $164.60  
  Purchase #3 $120.86   6.349%   $128.5334   $128.53   $128.55   $128.50  
  Purchase #4 $239.26   4.783%   $250.7038   $250.70   $250.70   $250.70  
  Purchase #5 $182.54   11.482%   $203.4992   $203.50   $203.50   $203.50  
  Purchase #6 $118.77   13.825%   $135.19   $135.19   $135.20   $135.20  
  Purchase #7 $39.98   4.601%   $41.8195   $41.82   $41.80   $41.80  
  7 purchase totals = $952.71       $1,028.5835   $1,028.58   $1,028.60   $1,028.50