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	$73.34	9.651%	$80.418	$80.42	$80.40	$80.40
Purchase #2	$59.38	3.573%	$61.5016	$61.50	$61.50	$61.50
Purchase #3	$243.38	9.284%	$265.9754	$265.98	$266.00	$266.00
Purchase #4	$134.69	13.459%	$152.8179	$152.82	$152.80	$152.80
Purchase #5	$186.97	12.749%	$210.8068	$210.81	$210.80	$210.80
Purchase #6	$127.74	11.188%	$142.0316	$142.03	$142.05	$142.00
Purchase #7	$174.89	11.661%	$195.2839	$195.28	$195.30	$195.30
7 purchase totals =	$1,000.39		$1,108.8352	$1,108.84	$1,108.85	$1,108.80