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	$232.58	13.526%	$264.0388	$264.04	$264.05	$264.00
Purchase #2	$232.53	7.851%	$250.7859	$250.79	$250.80	$250.80
Purchase #3	$222.59	6.399%	$236.8335	$236.83	$236.85	$236.80
Purchase #4	$80.64	3.444%	$83.4172	$83.42	$83.40	$83.40
Purchase #5	$26.83	7.834%	$28.9319	$28.93	$28.95	$28.90
Purchase #6	$99.48	5.327%	$104.7793	$104.78	$104.80	$104.80
Purchase #7	$33.64	3.449%	$34.8002	$34.80	$34.80	$34.80
7 purchase totals =	$928.29		$1,003.5868	$1,003.59	$1,003.65	$1,003.50