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	$79.32	7.382%	$85.1754	$85.18	$85.20	$85.20
Purchase #2	$202.83	3.254%	$209.4301	$209.43	$209.45	$209.40
Purchase #3	$168.45	9.820%	$184.9918	$184.99	$185.00	$185.00
Purchase #4	$93.50	12.742%	$105.4138	$105.41	$105.40	$105.40
Purchase #5	$31.54	7.330%	$33.8519	$33.85	$33.85	$33.90
Purchase #6	$74.43	4.132%	$77.5054	$77.51	$77.50	$77.50
Purchase #7	$37.95	10.621%	$41.9807	$41.98	$42.00	$42.00
7 purchase totals =	$688.02		$738.3491	$738.35	$738.40	$738.40