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 $105.88   10.648%   $117.1541   $117.15   $117.15   $117.20  
  Purchase #2 $13.47   6.346%   $14.3248   $14.32   $14.30   $14.30  
  Purchase #3 $143.99   6.493%   $153.3393   $153.34   $153.35   $153.30  
  Purchase #4 $204.26   13.855%   $232.5602   $232.56   $232.55   $232.60  
  Purchase #5 $167.40   5.749%   $177.0238   $177.02   $177.00   $177.00  
  Purchase #6 $62.68   8.328%   $67.9   $67.90   $67.90   $67.90  
  Purchase #7 $23.91   12.179%   $26.822   $26.82   $26.80   $26.80  
  7 purchase totals = $721.59       $789.1242   $789.11   $789.05   $789.10