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	$190.95	4.684%	$199.8941	$199.89	$199.90	$199.90
Purchase #2	$98.69	10.495%	$109.0475	$109.05	$109.05	$109.00
Purchase #3	$216.85	8.496%	$235.2736	$235.27	$235.25	$235.30
Purchase #4	$91.86	8.605%	$99.7646	$99.76	$99.75	$99.80
Purchase #5	$164.64	8.761%	$179.0641	$179.06	$179.05	$179.10
Purchase #6	$98.95	6.342%	$105.2254	$105.23	$105.25	$105.20
Purchase #7	$68.94	8.333%	$74.6848	$74.68	$74.70	$74.70
7 purchase totals =	$930.88		$1,002.9541	$1,002.94	$1,002.95	$1,003.00