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	$83.98	8.739%	$91.319	$91.32	$91.30	$91.30
Purchase #2	$74.87	11.851%	$83.7428	$83.74	$83.75	$83.70
Purchase #3	$46.84	3.104%	$48.2939	$48.29	$48.30	$48.30
Purchase #4	$196.43	11.400%	$218.823	$218.82	$218.80	$218.80
Purchase #5	$244.53	3.814%	$253.8564	$253.86	$253.85	$253.90
Purchase #6	$84.53	5.564%	$89.2332	$89.23	$89.25	$89.20
Purchase #7	$68.50	13.116%	$77.4845	$77.48	$77.50	$77.50
7 purchase totals =	$799.68		$862.7528	$862.74	$862.75	$862.70