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	$168.62	12.495%	$189.6891	$189.69	$189.70	$189.70
Purchase #2	$71.56	7.751%	$77.1066	$77.11	$77.10	$77.10
Purchase #3	$53.32	9.311%	$58.2846	$58.28	$58.30	$58.30
Purchase #4	$206.35	8.224%	$223.3202	$223.32	$223.30	$223.30
Purchase #5	$47.75	11.463%	$53.2236	$53.22	$53.20	$53.20
Purchase #6	$43.43	3.634%	$45.0082	$45.01	$45.00	$45.00
Purchase #7	$226.76	5.360%	$238.9143	$238.91	$238.90	$238.90
7 purchase totals =	$817.79		$885.5466	$885.54	$885.50	$885.50