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	$97.29	4.621%	$101.7858	$101.79	$101.80	$101.80
Purchase #2	$237.65	11.672%	$265.3885	$265.39	$265.40	$265.40
Purchase #3	$83.90	6.802%	$89.6069	$89.61	$89.60	$89.60
Purchase #4	$63.60	5.342%	$66.9975	$67.00	$67.00	$67.00
Purchase #5	$142.78	13.307%	$161.7797	$161.78	$161.80	$161.80
Purchase #6	$37.57	12.417%	$42.2351	$42.24	$42.25	$42.20
Purchase #7	$185.26	5.675%	$195.7735	$195.77	$195.75	$195.80
7 purchase totals =	$848.05		$923.5670	$923.58	$923.60	$923.60