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	$144.91	3.115%	$149.4239	$149.42	$149.40	$149.40
Purchase #2	$29.99	6.399%	$31.9091	$31.91	$31.90	$31.90
Purchase #3	$212.27	12.362%	$238.5108	$238.51	$238.50	$238.50
Purchase #4	$98.29	10.869%	$108.9731	$108.97	$108.95	$109.00
Purchase #5	$239.45	10.453%	$264.4797	$264.48	$264.50	$264.50
Purchase #6	$70.54	11.812%	$78.8722	$78.87	$78.85	$78.90
Purchase #7	$148.25	8.418%	$160.7297	$160.73	$160.75	$160.70
7 purchase totals =	$943.70		$1,032.8985	$1,032.89	$1,032.85	$1,032.90