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 $49.78   8.522%   $54.0223   $54.02   $54.00   $54.00  
  Purchase #2 $85.35   5.201%   $89.7891   $89.79   $89.80   $89.80  
  Purchase #3 $86.55   13.521%   $98.2524   $98.25   $98.25   $98.30  
  Purchase #4 $49.29   12.434%   $55.4187   $55.42   $55.40   $55.40  
  Purchase #5 $167.56   4.252%   $174.6847   $174.68   $174.70   $174.70  
  Purchase #6 $238.55   8.162%   $258.0205   $258.02   $258.00   $258.00  
  Purchase #7 $237.85   11.841%   $266.0138   $266.01   $266.00   $266.00  
  7 purchase totals = $914.93       $996.2015   $996.19   $996.15   $996.20