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	$200.90	10.700%	$222.3963	$222.40	$222.40	$222.40
Purchase #2	$169.62	12.182%	$190.2831	$190.28	$190.30	$190.30
Purchase #3	$224.65	8.282%	$243.2555	$243.26	$243.25	$243.30
Purchase #4	$41.46	8.432%	$44.9559	$44.96	$44.95	$45.00
Purchase #5	$195.92	6.363%	$208.3864	$208.39	$208.40	$208.40
Purchase #6	$153.72	7.753%	$165.6379	$165.64	$165.65	$165.60
Purchase #7	$158.57	11.516%	$176.8309	$176.83	$176.85	$176.80
7 purchase totals =	$1,144.84		$1,251.7460	$1,251.76	$1,251.80	$1,251.80