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	$240.84	12.288%	$270.4344	$270.43	$270.45	$270.40
Purchase #2	$144.68	10.650%	$160.0884	$160.09	$160.10	$160.10
Purchase #3	$58.89	3.277%	$60.8198	$60.82	$60.80	$60.80
Purchase #4	$19.52	6.709%	$20.8296	$20.83	$20.85	$20.80
Purchase #5	$168.61	12.850%	$190.2764	$190.28	$190.30	$190.30
Purchase #6	$135.34	4.369%	$141.253	$141.25	$141.25	$141.30
Purchase #7	$245.56	6.580%	$261.7178	$261.72	$261.70	$261.70
7 purchase totals =	$1,013.44		$1,105.4194	$1,105.42	$1,105.45	$1,105.40