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	$200.82	12.371%	$225.6634	$225.66	$225.65	$225.70
Purchase #2	$209.56	6.376%	$222.9215	$222.92	$222.90	$222.90
Purchase #3	$82.92	8.751%	$90.1763	$90.18	$90.20	$90.20
Purchase #4	$206.95	6.415%	$220.2258	$220.23	$220.25	$220.20
Purchase #5	$92.66	8.801%	$100.815	$100.82	$100.80	$100.80
Purchase #6	$82.41	6.861%	$88.0642	$88.06	$88.05	$88.10
Purchase #7	$59.28	11.292%	$65.9739	$65.97	$65.95	$66.00
7 purchase totals =	$934.60		$1,013.8401	$1,013.84	$1,013.80	$1,013.90