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 $245.53   8.267%   $265.828   $265.83   $265.85   $265.80  
  Purchase #2 $136.27   12.605%   $153.4468   $153.45   $153.45   $153.40  
  Purchase #3 $40.36   3.825%   $41.9038   $41.90   $41.90   $41.90  
  Purchase #4 $237.89   12.795%   $268.328   $268.33   $268.35   $268.30  
  Purchase #5 $14.84   8.191%   $16.0555   $16.06   $16.05   $16.10  
  Purchase #6 $226.29   6.496%   $240.9898   $240.99   $241.00   $241.00  
  Purchase #7 $32.42   13.139%   $36.6797   $36.68   $36.70   $36.70  
  7 purchase totals = $933.60       $1,023.2316   $1,023.24   $1,023.30   $1,023.20