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	$20.36	7.614%	$21.9102	$21.91	$21.90	$21.90
Purchase #2	$91.63	12.107%	$102.7236	$102.72	$102.70	$102.70
Purchase #3	$235.47	11.300%	$262.0781	$262.08	$262.10	$262.10
Purchase #4	$60.30	8.514%	$65.4339	$65.43	$65.45	$65.40
Purchase #5	$190.77	3.193%	$196.8613	$196.86	$196.85	$196.90
Purchase #6	$53.48	3.510%	$55.3571	$55.36	$55.35	$55.40
Purchase #7	$222.94	12.532%	$250.8788	$250.88	$250.90	$250.90
7 purchase totals =	$874.95		$955.2430	$955.24	$955.25	$955.30