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	$78.73	13.254%	$89.1649	$89.16	$89.15	$89.20
Purchase #2	$15.45	13.212%	$17.4913	$17.49	$17.50	$17.50
Purchase #3	$53.80	4.400%	$56.1672	$56.17	$56.15	$56.20
Purchase #4	$86.57	3.790%	$89.851	$89.85	$89.85	$89.90
Purchase #5	$16.84	4.744%	$17.6389	$17.64	$17.65	$17.60
Purchase #6	$73.49	8.383%	$79.6507	$79.65	$79.65	$79.70
Purchase #7	$137.40	11.174%	$152.7531	$152.75	$152.75	$152.80
7 purchase totals =	$462.28		$502.7171	$502.71	$502.70	$502.90