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 $47.84   11.826%   $53.4976   $53.50   $53.50   $53.50  
  Purchase #2 $164.66   3.509%   $170.4379   $170.44   $170.45   $170.40  
  Purchase #3 $129.67   6.447%   $138.0298   $138.03   $138.05   $138.00  
  Purchase #4 $97.85   11.148%   $108.7583   $108.76   $108.75   $108.80  
  Purchase #5 $226.28   10.838%   $250.8042   $250.80   $250.80   $250.80  
  Purchase #6 $30.29   11.399%   $33.7428   $33.74   $33.75   $33.70  
  Purchase #7 $234.99   9.692%   $257.7652   $257.77   $257.75   $257.80  
  7 purchase totals = $931.58       $1,013.0358   $1,013.04   $1,013.05   $1,013.00