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	$157.75	5.529%	$166.472	$166.47	$166.45	$166.50
Purchase #2	$121.54	9.690%	$133.3172	$133.32	$133.30	$133.30
Purchase #3	$35.43	10.148%	$39.0254	$39.03	$39.05	$39.00
Purchase #4	$82.75	5.533%	$87.3286	$87.33	$87.35	$87.30
Purchase #5	$122.40	6.620%	$130.5029	$130.50	$130.50	$130.50
Purchase #6	$135.66	7.819%	$146.2673	$146.27	$146.25	$146.30
Purchase #7	$85.65	4.871%	$89.822	$89.82	$89.80	$89.80
7 purchase totals =	$741.18		$792.7354	$792.74	$792.70	$792.70