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	$37.75	11.811%	$42.2087	$42.21	$42.20	$42.20
Purchase #2	$159.64	8.862%	$173.7873	$173.79	$173.80	$173.80
Purchase #3	$71.62	7.512%	$77.0001	$77.00	$77.00	$77.00
Purchase #4	$96.54	13.194%	$109.2775	$109.28	$109.30	$109.30
Purchase #5	$191.27	3.290%	$197.5628	$197.56	$197.55	$197.60
Purchase #6	$53.48	7.207%	$57.3343	$57.33	$57.35	$57.30
Purchase #7	$78.93	13.567%	$89.6384	$89.64	$89.65	$89.60
7 purchase totals =	$689.23		$746.8091	$746.81	$746.85	$746.80