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	$118.63	9.409%	$129.7919	$129.79	$129.80	$129.80
Purchase #2	$219.60	12.728%	$247.5507	$247.55	$247.55	$247.60
Purchase #3	$172.35	6.236%	$183.0977	$183.10	$183.10	$183.10
Purchase #4	$150.89	5.636%	$159.3942	$159.39	$159.40	$159.40
Purchase #5	$55.34	7.527%	$59.5054	$59.51	$59.50	$59.50
Purchase #6	$183.51	6.819%	$196.0235	$196.02	$196.00	$196.00
Purchase #7	$105.72	8.757%	$114.9779	$114.98	$115.00	$115.00
7 purchase totals =	$1,006.04		$1,090.3413	$1,090.34	$1,090.35	$1,090.40