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 $124.31   13.246%   $140.7761   $140.78   $140.80   $140.80  
  Purchase #2 $164.66   13.530%   $186.9385   $186.94   $186.95   $186.90  
  Purchase #3 $151.47   12.461%   $170.3447   $170.34   $170.35   $170.30  
  Purchase #4 $55.81   5.495%   $58.8768   $58.88   $58.90   $58.90  
  Purchase #5 $164.73   12.176%   $184.7875   $184.79   $184.80   $184.80  
  Purchase #6 $190.48   13.622%   $216.4272   $216.43   $216.45   $216.40  
  Purchase #7 $111.46   6.574%   $118.7874   $118.79   $118.80   $118.80  
  7 purchase totals = $962.92       $1,076.9382   $1,076.95   $1,077.05   $1,076.90