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 $47.96   12.449%   $53.9305   $53.93   $53.95   $53.90  
  Purchase #2 $58.43   4.389%   $60.9945   $60.99   $61.00   $61.00  
  Purchase #3 $26.45   11.493%   $29.4899   $29.49   $29.50   $29.50  
  Purchase #4 $182.37   13.477%   $206.948   $206.95   $206.95   $206.90  
  Purchase #5 $235.33   9.531%   $257.7593   $257.76   $257.75   $257.80  
  Purchase #6 $124.94   10.712%   $138.3236   $138.32   $138.30   $138.30  
  Purchase #7 $108.85   12.523%   $122.4813   $122.48   $122.50   $122.50  
  7 purchase totals = $784.33       $869.9271   $869.92   $869.95   $869.90