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	$22.90	10.498%	$25.304	$25.30	$25.30	$25.30
Purchase #2	$141.44	13.790%	$160.9446	$160.94	$160.95	$160.90
Purchase #3	$83.99	8.264%	$90.9309	$90.93	$90.95	$90.90
Purchase #4	$140.99	5.546%	$148.8093	$148.81	$148.80	$148.80
Purchase #5	$72.83	7.286%	$78.1364	$78.14	$78.15	$78.10
Purchase #6	$94.61	5.204%	$99.5335	$99.53	$99.55	$99.50
Purchase #7	$84.63	10.774%	$93.748	$93.75	$93.75	$93.70
7 purchase totals =	$641.39		$697.4067	$697.40	$697.45	$697.20