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	$90.73	8.760%	$98.6779	$98.68	$98.70	$98.70
Purchase #2	$76.81	12.394%	$86.3298	$86.33	$86.35	$86.30
Purchase #3	$6.78	10.434%	$7.4874	$7.49	$7.50	$7.50
Purchase #4	$209.66	9.322%	$229.2045	$229.20	$229.20	$229.20
Purchase #5	$210.82	5.697%	$222.8304	$222.83	$222.85	$222.80
Purchase #6	$72.65	11.579%	$81.0621	$81.06	$81.05	$81.10
Purchase #7	$245.45	4.398%	$256.2449	$256.24	$256.25	$256.20
7 purchase totals =	$912.90		$981.8370	$981.83	$981.90	$981.80