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 $232.69   3.758%   $241.4345   $241.43   $241.45   $241.40  
  Purchase #2 $176.76   10.324%   $195.0087   $195.01   $195.00   $195.00  
  Purchase #3 $110.66   7.846%   $119.3424   $119.34   $119.35   $119.30  
  Purchase #4 $104.54   8.783%   $113.7217   $113.72   $113.70   $113.70  
  Purchase #5 $59.26   10.305%   $65.3667   $65.37   $65.35   $65.40  
  Purchase #6 $47.49   10.853%   $52.6441   $52.64   $52.65   $52.60  
  Purchase #7 $217.70   5.849%   $230.4333   $230.43   $230.45   $230.40  
  7 purchase totals = $949.10       $1,017.9514   $1,017.94   $1,017.95   $1,017.80