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	$17.86	10.790%	$19.7871	$19.79	$19.80	$19.80
Purchase #2	$153.57	11.400%	$171.077	$171.08	$171.10	$171.10
Purchase #3	$200.75	10.367%	$221.5618	$221.56	$221.55	$221.60
Purchase #4	$48.48	8.860%	$52.7753	$52.78	$52.80	$52.80
Purchase #5	$98.58	7.317%	$105.7931	$105.79	$105.80	$105.80
Purchase #6	$160.43	8.659%	$174.3216	$174.32	$174.30	$174.30
Purchase #7	$48.88	11.425%	$54.4645	$54.46	$54.45	$54.50
7 purchase totals =	$728.55		$799.7804	$799.78	$799.80	$799.90