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	$81.76	9.126%	$89.2214	$89.22	$89.20	$89.20
Purchase #2	$72.48	9.550%	$79.4018	$79.40	$79.40	$79.40
Purchase #3	$112.37	6.829%	$120.0437	$120.04	$120.05	$120.00
Purchase #4	$167.59	7.829%	$180.7106	$180.71	$180.70	$180.70
Purchase #5	$35.81	7.272%	$38.4141	$38.41	$38.40	$38.40
Purchase #6	$114.33	7.562%	$122.9756	$122.98	$123.00	$123.00
Purchase #7	$37.37	12.860%	$42.1758	$42.18	$42.20	$42.20
7 purchase totals =	$621.71		$672.9430	$672.94	$672.95	$672.90