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	$77.29	7.797%	$83.3163	$83.32	$83.30	$83.30
Purchase #2	$59.60	9.772%	$65.4241	$65.42	$65.40	$65.40
Purchase #3	$156.72	3.702%	$162.5218	$162.52	$162.50	$162.50
Purchase #4	$85.99	3.632%	$89.1132	$89.11	$89.10	$89.10
Purchase #5	$118.73	9.107%	$129.5427	$129.54	$129.55	$129.50
Purchase #6	$139.61	11.465%	$155.6163	$155.62	$155.60	$155.60
Purchase #7	$186.55	6.172%	$198.0639	$198.06	$198.05	$198.10
7 purchase totals =	$824.49		$883.5983	$883.59	$883.50	$883.50