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	$74.81	4.734%	$78.3515	$78.35	$78.35	$78.40
Purchase #2	$87.60	3.610%	$90.7624	$90.76	$90.75	$90.80
Purchase #3	$25.59	9.662%	$28.0625	$28.06	$28.05	$28.10
Purchase #4	$82.56	8.718%	$89.7576	$89.76	$89.75	$89.80
Purchase #5	$171.98	6.242%	$182.715	$182.72	$182.70	$182.70
Purchase #6	$122.90	3.627%	$127.3576	$127.36	$127.35	$127.40
Purchase #7	$243.43	4.107%	$253.4277	$253.43	$253.45	$253.40
7 purchase totals =	$808.87		$850.4343	$850.44	$850.40	$850.60