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	$210.95	7.153%	$226.0393	$226.04	$226.05	$226.00
Purchase #2	$37.56	11.355%	$41.8249	$41.82	$41.80	$41.80
Purchase #3	$134.59	12.824%	$151.8498	$151.85	$151.85	$151.80
Purchase #4	$24.75	11.201%	$27.5222	$27.52	$27.50	$27.50
Purchase #5	$159.41	7.826%	$171.8854	$171.89	$171.90	$171.90
Purchase #6	$52.89	6.313%	$56.2289	$56.23	$56.25	$56.20
Purchase #7	$245.84	7.520%	$264.3272	$264.33	$264.35	$264.30
7 purchase totals =	$865.99		$939.6777	$939.68	$939.70	$939.50