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	$110.84	8.250%	$119.9843	$119.98	$120.00	$120.00
Purchase #2	$58.64	11.252%	$65.2382	$65.24	$65.25	$65.20
Purchase #3	$129.43	11.507%	$144.3235	$144.32	$144.30	$144.30
Purchase #4	$18.48	4.642%	$19.3378	$19.34	$19.35	$19.30
Purchase #5	$137.76	10.450%	$152.1559	$152.16	$152.15	$152.20
Purchase #6	$41.31	7.780%	$44.5239	$44.52	$44.50	$44.50
Purchase #7	$90.89	3.154%	$93.7567	$93.76	$93.75	$93.80
7 purchase totals =	$587.35		$639.3203	$639.32	$639.30	$639.30