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 $89.34   9.771%   $98.0694   $98.07   $98.05   $98.10  
  Purchase #2 $204.38   13.839%   $232.6641   $232.66   $232.65   $232.70  
  Purchase #3 $120.83   4.338%   $126.0716   $126.07   $126.05   $126.10  
  Purchase #4 $234.88   13.485%   $266.5536   $266.55   $266.55   $266.60  
  Purchase #5 $92.99   8.480%   $100.8756   $100.88   $100.90   $100.90  
  Purchase #6 $169.47   5.651%   $179.0467   $179.05   $179.05   $179.00  
  Purchase #7 $104.84   6.599%   $111.7584   $111.76   $111.75   $111.80  
  7 purchase totals = $1,016.73       $1,115.0394   $1,115.04   $1,115.00   $1,115.20