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 $179.79   10.830%   $199.2613   $199.26   $199.25   $199.30  
  Purchase #2 $52.84   11.270%   $58.7951   $58.80   $58.80   $58.80  
  Purchase #3 $189.61   4.370%   $197.896   $197.90   $197.90   $197.90  
  Purchase #4 $62.98   11.581%   $70.2737   $70.27   $70.25   $70.30  
  Purchase #5 $208.91   6.679%   $222.8631   $222.86   $222.85   $222.90  
  Purchase #6 $126.61   9.745%   $138.9481   $138.95   $138.95   $138.90  
  Purchase #7 $238.90   4.238%   $249.0246   $249.02   $249.00   $249.00  
  7 purchase totals = $1,059.64       $1,137.0619   $1,137.06   $1,137.00   $1,137.10