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	$12.37	10.540%	$13.6738	$13.67	$13.65	$13.70
Purchase #2	$206.47	4.336%	$215.4225	$215.42	$215.40	$215.40
Purchase #3	$118.71	7.818%	$127.9907	$127.99	$128.00	$128.00
Purchase #4	$78.62	4.375%	$82.0596	$82.06	$82.05	$82.10
Purchase #5	$212.44	4.173%	$221.3051	$221.31	$221.30	$221.30
Purchase #6	$103.54	9.802%	$113.689	$113.69	$113.70	$113.70
Purchase #7	$88.48	11.238%	$98.4234	$98.42	$98.40	$98.40
7 purchase totals =	$820.63		$872.5641	$872.56	$872.50	$872.60