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 $223.30   12.224%   $250.5962   $250.60   $250.60   $250.60  
  Purchase #2 $130.94   8.462%   $142.0201   $142.02   $142.00   $142.00  
  Purchase #3 $157.39   10.580%   $174.0419   $174.04   $174.05   $174.00  
  Purchase #4 $86.79   9.168%   $94.7469   $94.75   $94.75   $94.70  
  Purchase #5 $112.99   8.553%   $122.654   $122.65   $122.65   $122.70  
  Purchase #6 $187.91   3.560%   $194.5996   $194.60   $194.60   $194.60  
  Purchase #7 $87.32   12.632%   $98.3503   $98.35   $98.35   $98.40  
  7 purchase totals = $986.64       $1,077.0090   $1,077.01   $1,077.00   $1,077.00