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 $230.34   12.874%   $259.994   $259.99   $260.00   $260.00  
  Purchase #2 $80.93   5.503%   $85.3836   $85.38   $85.40   $85.40  
  Purchase #3 $165.45   4.576%   $173.021   $173.02   $173.00   $173.00  
  Purchase #4 $193.39   7.478%   $207.8517   $207.85   $207.85   $207.90  
  Purchase #5 $145.54   5.269%   $153.2085   $153.21   $153.20   $153.20  
  Purchase #6 $130.45   11.259%   $145.1374   $145.14   $145.15   $145.10  
  Purchase #7 $194.75   4.210%   $202.949   $202.95   $202.95   $202.90  
  7 purchase totals = $1,140.85       $1,227.5452   $1,227.54   $1,227.55   $1,227.50