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	$85.45	4.230%	$89.0645	$89.06	$89.05	$89.10
Purchase #2	$150.41	3.804%	$156.1316	$156.13	$156.15	$156.10
Purchase #3	$93.57	6.555%	$99.7035	$99.70	$99.70	$99.70
Purchase #4	$199.69	9.542%	$218.7444	$218.74	$218.75	$218.70
Purchase #5	$243.33	4.596%	$254.5134	$254.51	$254.50	$254.50
Purchase #6	$43.47	4.539%	$45.4431	$45.44	$45.45	$45.40
Purchase #7	$21.73	13.242%	$24.6075	$24.61	$24.60	$24.60
7 purchase totals =	$837.65		$888.2080	$888.19	$888.20	$888.10