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	$125.93	13.190%	$142.5402	$142.54	$142.55	$142.50
Purchase #2	$90.86	9.697%	$99.6707	$99.67	$99.65	$99.70
Purchase #3	$134.87	11.399%	$150.2438	$150.24	$150.25	$150.20
Purchase #4	$132.48	3.544%	$137.1751	$137.18	$137.20	$137.20
Purchase #5	$250.90	9.336%	$274.324	$274.32	$274.30	$274.30
Purchase #6	$137.33	10.358%	$151.5546	$151.55	$151.55	$151.60
Purchase #7	$155.36	7.623%	$167.2031	$167.20	$167.20	$167.20
7 purchase totals =	$1,027.73		$1,122.7115	$1,122.70	$1,122.70	$1,122.70