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	$55.79	7.362%	$59.8973	$59.90	$59.90	$59.90
Purchase #2	$181.54	11.813%	$202.9853	$202.99	$203.00	$203.00
Purchase #3	$233.38	9.225%	$254.9093	$254.91	$254.90	$254.90
Purchase #4	$132.48	7.458%	$142.3604	$142.36	$142.35	$142.40
Purchase #5	$146.35	3.607%	$151.6288	$151.63	$151.65	$151.60
Purchase #6	$73.82	10.485%	$81.56	$81.56	$81.55	$81.60
Purchase #7	$233.34	8.570%	$253.3372	$253.34	$253.35	$253.30
7 purchase totals =	$1,056.70		$1,146.6783	$1,146.69	$1,146.70	$1,146.70