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 $241.48   11.616%   $269.5303   $269.53   $269.55   $269.50  
  Purchase #2 $110.85   8.284%   $120.0328   $120.03   $120.05   $120.00  
  Purchase #3 $135.75   4.163%   $141.4013   $141.40   $141.40   $141.40  
  Purchase #4 $115.68   13.770%   $131.6091   $131.61   $131.60   $131.60  
  Purchase #5 $54.84   9.110%   $59.8359   $59.84   $59.85   $59.80  
  Purchase #6 $41.30   6.505%   $43.9866   $43.99   $44.00   $44.00  
  Purchase #7 $233.53   11.309%   $259.9399   $259.94   $259.95   $259.90  
  7 purchase totals = $933.43       $1,026.3359   $1,026.34   $1,026.40   $1,026.20