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	$168.90	6.638%	$180.1116	$180.11	$180.10	$180.10
Purchase #2	$19.88	7.180%	$21.3074	$21.31	$21.30	$21.30
Purchase #3	$94.48	9.586%	$103.5369	$103.54	$103.55	$103.50
Purchase #4	$172.91	6.334%	$183.8621	$183.86	$183.85	$183.90
Purchase #5	$224.52	7.844%	$242.1313	$242.13	$242.15	$242.10
Purchase #6	$227.73	11.168%	$253.1629	$253.16	$253.15	$253.20
Purchase #7	$7.28	6.690%	$7.767	$7.77	$7.75	$7.80
7 purchase totals =	$915.70		$991.8792	$991.88	$991.85	$991.90