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 $227.45   8.627%   $247.0721   $247.07   $247.05   $247.10  
  Purchase #2 $232.57   3.346%   $240.3518   $240.35   $240.35   $240.40  
  Purchase #3 $240.76   7.400%   $258.5762   $258.58   $258.60   $258.60  
  Purchase #4 $165.40   6.339%   $175.8847   $175.88   $175.90   $175.90  
  Purchase #5 $208.25   11.403%   $231.9967   $232.00   $232.00   $232.00  
  Purchase #6 $178.60   4.727%   $187.0424   $187.04   $187.05   $187.00  
  Purchase #7 $176.96   3.385%   $182.9501   $182.95   $182.95   $183.00  
  7 purchase totals = $1,429.99       $1,523.8740   $1,523.87   $1,523.90   $1,524.00