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 $177.33   4.744%   $185.7425   $185.74   $185.75   $185.70  
  Purchase #2 $250.42   6.528%   $266.7674   $266.77   $266.75   $266.80  
  Purchase #3 $83.97   13.696%   $95.4705   $95.47   $95.45   $95.50  
  Purchase #4 $174.32   5.870%   $184.5526   $184.55   $184.55   $184.60  
  Purchase #5 $84.36   4.300%   $87.9875   $87.99   $88.00   $88.00  
  Purchase #6 $94.87   6.470%   $101.0081   $101.01   $101.00   $101.00  
  Purchase #7 $51.66   5.744%   $54.6274   $54.63   $54.65   $54.60  
  7 purchase totals = $916.93       $976.1560   $976.16   $976.15   $976.20