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	$147.35	13.438%	$167.1509	$167.15	$167.15	$167.20
Purchase #2	$172.72	3.697%	$179.1055	$179.11	$179.10	$179.10
Purchase #3	$124.30	5.753%	$131.451	$131.45	$131.45	$131.50
Purchase #4	$223.78	11.520%	$249.5595	$249.56	$249.55	$249.60
Purchase #5	$72.98	9.219%	$79.708	$79.71	$79.70	$79.70
Purchase #6	$82.79	6.862%	$88.471	$88.47	$88.45	$88.50
Purchase #7	$165.59	11.776%	$185.0899	$185.09	$185.10	$185.10
7 purchase totals =	$989.51		$1,080.5358	$1,080.54	$1,080.50	$1,080.70