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	$90.89	12.684%	$102.4185	$102.42	$102.40	$102.40
Purchase #2	$26.90	6.172%	$28.5603	$28.56	$28.55	$28.60
Purchase #3	$58.87	3.145%	$60.7215	$60.72	$60.70	$60.70
Purchase #4	$180.63	8.692%	$196.3304	$196.33	$196.35	$196.30
Purchase #5	$222.67	12.171%	$249.7712	$249.77	$249.75	$249.80
Purchase #6	$143.53	13.475%	$162.8707	$162.87	$162.85	$162.90
Purchase #7	$232.35	13.273%	$263.1898	$263.19	$263.20	$263.20
7 purchase totals =	$955.84		$1,063.8624	$1,063.86	$1,063.80	$1,063.90