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	$236.31	12.270%	$265.3052	$265.31	$265.30	$265.30
Purchase #2	$85.71	10.549%	$94.7515	$94.75	$94.75	$94.80
Purchase #3	$133.83	10.443%	$147.8059	$147.81	$147.80	$147.80
Purchase #4	$135.26	6.700%	$144.3224	$144.32	$144.30	$144.30
Purchase #5	$101.34	10.318%	$111.7963	$111.80	$111.80	$111.80
Purchase #6	$161.77	5.699%	$170.9893	$170.99	$171.00	$171.00
Purchase #7	$72.34	11.597%	$80.7293	$80.73	$80.75	$80.70
7 purchase totals =	$926.56		$1,015.6999	$1,015.71	$1,015.70	$1,015.70