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	$78.91	13.399%	$89.4832	$89.48	$89.50	$89.50
Purchase #2	$188.94	5.399%	$199.1409	$199.14	$199.15	$199.10
Purchase #3	$184.95	13.457%	$209.8387	$209.84	$209.85	$209.80
Purchase #4	$65.91	4.840%	$69.1	$69.10	$69.10	$69.10
Purchase #5	$67.53	3.472%	$69.8746	$69.87	$69.85	$69.90
Purchase #6	$209.96	6.459%	$223.5213	$223.52	$223.50	$223.50
Purchase #7	$104.64	11.292%	$116.4559	$116.46	$116.45	$116.50
7 purchase totals =	$900.84		$977.4146	$977.41	$977.40	$977.40