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	$83.89	6.107%	$89.0132	$89.01	$89.00	$89.00
Purchase #2	$36.69	6.735%	$39.1611	$39.16	$39.15	$39.20
Purchase #3	$83.28	5.375%	$87.7563	$87.76	$87.75	$87.80
Purchase #4	$229.36	10.538%	$253.53	$253.53	$253.55	$253.50
Purchase #5	$193.43	10.406%	$213.5583	$213.56	$213.55	$213.60
Purchase #6	$227.95	3.233%	$235.3196	$235.32	$235.30	$235.30
Purchase #7	$189.33	13.766%	$215.3932	$215.39	$215.40	$215.40
7 purchase totals =	$1,043.93		$1,133.7317	$1,133.73	$1,133.70	$1,133.80