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 $191.89   7.869%   $206.9898   $206.99   $207.00   $207.00  
  Purchase #2 $155.47   12.507%   $174.9146   $174.91   $174.90   $174.90  
  Purchase #3 $58.79   11.693%   $65.6643   $65.66   $65.65   $65.70  
  Purchase #4 $90.71   3.567%   $93.9456   $93.95   $93.95   $93.90  
  Purchase #5 $237.44   5.501%   $250.5016   $250.50   $250.50   $250.50  
  Purchase #6 $129.76   11.351%   $144.4891   $144.49   $144.50   $144.50  
  Purchase #7 $122.90   4.112%   $127.9536   $127.95   $127.95   $128.00  
  7 purchase totals = $986.96       $1,064.4586   $1,064.45   $1,064.45   $1,064.50