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 $60.81   13.749%   $69.1708   $69.17   $69.15   $69.20  
  Purchase #2 $227.62   13.673%   $258.7425   $258.74   $258.75   $258.70  
  Purchase #3 $59.55   9.234%   $65.0488   $65.05   $65.05   $65.00  
  Purchase #4 $83.68   3.598%   $86.6908   $86.69   $86.70   $86.70  
  Purchase #5 $11.51   6.226%   $12.2266   $12.23   $12.25   $12.20  
  Purchase #6 $156.77   5.395%   $165.2277   $165.23   $165.25   $165.20  
  Purchase #7 $142.82   11.620%   $159.4157   $159.42   $159.40   $159.40  
  7 purchase totals = $742.76       $816.5229   $816.53   $816.55   $816.40