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	$182.52	4.276%	$190.3246	$190.32	$190.30	$190.30
Purchase #2	$133.76	6.591%	$142.5761	$142.58	$142.60	$142.60
Purchase #3	$174.88	6.277%	$185.8572	$185.86	$185.85	$185.90
Purchase #4	$190.26	12.128%	$213.3347	$213.33	$213.35	$213.30
Purchase #5	$51.41	6.245%	$54.6206	$54.62	$54.60	$54.60
Purchase #6	$209.31	13.790%	$238.1738	$238.17	$238.15	$238.20
Purchase #7	$214.51	9.468%	$234.8198	$234.82	$234.80	$234.80
7 purchase totals =	$1,156.65		$1,259.7068	$1,259.70	$1,259.65	$1,259.70