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	$33.47	12.288%	$37.5828	$37.58	$37.60	$37.60
Purchase #2	$197.69	6.189%	$209.925	$209.93	$209.95	$209.90
Purchase #3	$89.83	12.478%	$101.039	$101.04	$101.05	$101.00
Purchase #4	$175.31	8.224%	$189.7275	$189.73	$189.75	$189.70
Purchase #5	$59.33	8.111%	$64.1423	$64.14	$64.15	$64.10
Purchase #6	$196.98	3.838%	$204.5401	$204.54	$204.55	$204.50
Purchase #7	$155.67	8.507%	$168.9128	$168.91	$168.90	$168.90
7 purchase totals =	$908.28		$975.8695	$975.87	$975.95	$975.70