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 $184.75   4.858%   $193.7252   $193.73   $193.75   $193.70  
  Purchase #2 $200.74   10.108%   $221.0308   $221.03   $221.05   $221.00  
  Purchase #3 $40.99   8.305%   $44.3942   $44.39   $44.40   $44.40  
  Purchase #4 $55.26   4.252%   $57.6097   $57.61   $57.60   $57.60  
  Purchase #5 $11.87   4.551%   $12.4102   $12.41   $12.40   $12.40  
  Purchase #6 $86.85   7.582%   $93.435   $93.44   $93.45   $93.40  
  Purchase #7 $174.80   10.814%   $193.7029   $193.70   $193.70   $193.70  
  7 purchase totals = $755.26       $816.3080   $816.31   $816.35   $816.20