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	$79.73	4.508%	$83.3242	$83.32	$83.30	$83.30
Purchase #2	$195.64	11.122%	$217.3991	$217.40	$217.40	$217.40
Purchase #3	$152.78	6.307%	$162.4158	$162.42	$162.40	$162.40
Purchase #4	$120.74	12.223%	$135.4981	$135.50	$135.50	$135.50
Purchase #5	$72.82	13.489%	$82.6427	$82.64	$82.65	$82.60
Purchase #6	$179.33	10.781%	$198.6636	$198.66	$198.65	$198.70
Purchase #7	$55.66	6.825%	$59.4588	$59.46	$59.45	$59.50
7 purchase totals =	$856.70		$939.4023	$939.40	$939.35	$939.40