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	$125.81	12.373%	$141.3765	$141.38	$141.40	$141.40
Purchase #2	$65.70	6.680%	$70.0888	$70.09	$70.10	$70.10
Purchase #3	$224.84	10.483%	$248.41	$248.41	$248.40	$248.40
Purchase #4	$224.58	7.386%	$241.1675	$241.17	$241.15	$241.20
Purchase #5	$94.36	5.582%	$99.6272	$99.63	$99.65	$99.60
Purchase #6	$91.54	8.447%	$99.2724	$99.27	$99.25	$99.30
Purchase #7	$193.47	3.649%	$200.5297	$200.53	$200.55	$200.50
7 purchase totals =	$1,020.30		$1,100.4721	$1,100.48	$1,100.50	$1,100.50