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 $41.43   11.536%   $46.2094   $46.21   $46.20   $46.20  
  Purchase #2 $19.42   7.866%   $20.9476   $20.95   $20.95   $20.90  
  Purchase #3 $151.72   8.606%   $164.777   $164.78   $164.80   $164.80  
  Purchase #4 $82.53   4.821%   $86.5088   $86.51   $86.50   $86.50  
  Purchase #5 $232.72   6.272%   $247.3162   $247.32   $247.30   $247.30  
  Purchase #6 $229.69   12.748%   $258.9709   $258.97   $258.95   $259.00  
  Purchase #7 $194.55   3.354%   $201.0752   $201.08   $201.10   $201.10  
  7 purchase totals = $952.06       $1,025.8051   $1,025.82   $1,025.80   $1,025.80