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	$90.66	10.215%	$99.9209	$99.92	$99.90	$99.90
Purchase #2	$243.73	10.572%	$269.4971	$269.50	$269.50	$269.50
Purchase #3	$82.89	8.296%	$89.7666	$89.77	$89.75	$89.80
Purchase #4	$211.91	9.165%	$231.3316	$231.33	$231.35	$231.30
Purchase #5	$81.36	8.826%	$88.5408	$88.54	$88.55	$88.50
Purchase #6	$244.73	9.155%	$267.135	$267.14	$267.15	$267.10
Purchase #7	$132.64	6.347%	$141.0587	$141.06	$141.05	$141.10
7 purchase totals =	$1,087.92		$1,187.2507	$1,187.26	$1,187.25	$1,187.20