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 $88.55   10.860%   $98.1665   $98.17   $98.15   $98.20  
  Purchase #2 $188.97   12.815%   $213.1865   $213.19   $213.20   $213.20  
  Purchase #3 $55.84   3.186%   $57.6191   $57.62   $57.60   $57.60  
  Purchase #4 $175.43   9.781%   $192.5888   $192.59   $192.60   $192.60  
  Purchase #5 $42.53   13.698%   $48.3558   $48.36   $48.35   $48.40  
  Purchase #6 $210.57   6.305%   $223.8464   $223.85   $223.85   $223.80  
  Purchase #7 $208.27   6.301%   $221.3931   $221.39   $221.40   $221.40  
  7 purchase totals = $970.16       $1,055.1562   $1,055.17   $1,055.15   $1,055.20