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 $53.93   7.618%   $58.0384   $58.04   $58.05   $58.00  
  Purchase #2 $89.89   12.459%   $101.0894   $101.09   $101.10   $101.10  
  Purchase #3 $185.88   11.310%   $206.903   $206.90   $206.90   $206.90  
  Purchase #4 $249.64   10.467%   $275.7698   $275.77   $275.75   $275.80  
  Purchase #5 $187.78   11.239%   $208.8846   $208.88   $208.90   $208.90  
  Purchase #6 $41.94   12.804%   $47.31   $47.31   $47.30   $47.30  
  Purchase #7 $56.39   9.573%   $61.7882   $61.79   $61.80   $61.80  
  7 purchase totals = $865.45       $959.7834   $959.78   $959.80   $959.80