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	$99.74	5.672%	$105.3973	$105.40	$105.40	$105.40
Purchase #2	$202.35	3.168%	$208.7604	$208.76	$208.75	$208.80
Purchase #3	$157.37	7.294%	$168.8486	$168.85	$168.85	$168.80
Purchase #4	$100.72	8.842%	$109.6257	$109.63	$109.65	$109.60
Purchase #5	$64.43	13.274%	$72.9824	$72.98	$73.00	$73.00
Purchase #6	$246.59	13.237%	$279.2311	$279.23	$279.25	$279.20
Purchase #7	$223.63	9.575%	$245.0426	$245.04	$245.05	$245.00
7 purchase totals =	$1,094.83		$1,189.8881	$1,189.89	$1,189.95	$1,189.80