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 $161.65   8.441%   $175.2949   $175.29   $175.30   $175.30  
  Purchase #2 $235.28   8.543%   $255.38   $255.38   $255.40   $255.40  
  Purchase #3 $202.42   13.413%   $229.5706   $229.57   $229.55   $229.60  
  Purchase #4 $98.63   9.506%   $108.0058   $108.01   $108.00   $108.00  
  Purchase #5 $104.49   13.625%   $118.7268   $118.73   $118.75   $118.70  
  Purchase #6 $54.63   3.522%   $56.5541   $56.55   $56.55   $56.60  
  Purchase #7 $26.37   10.106%   $29.035   $29.04   $29.05   $29.00  
  7 purchase totals = $883.47       $972.5672   $972.57   $972.60   $972.60