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	$78.48	12.530%	$88.3135	$88.31	$88.30	$88.30
Purchase #2	$33.33	7.438%	$35.8091	$35.81	$35.80	$35.80
Purchase #3	$60.81	6.637%	$64.846	$64.85	$64.85	$64.80
Purchase #4	$155.48	6.844%	$166.1211	$166.12	$166.10	$166.10
Purchase #5	$186.46	5.387%	$196.5046	$196.50	$196.50	$196.50
Purchase #6	$47.37	12.128%	$53.115	$53.12	$53.10	$53.10
Purchase #7	$24.82	9.411%	$27.1558	$27.16	$27.15	$27.20
7 purchase totals =	$586.75		$631.8651	$631.87	$631.80	$631.80