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	$55.65	11.213%	$61.89	$61.89	$61.90	$61.90
Purchase #2	$232.57	7.575%	$250.1872	$250.19	$250.20	$250.20
Purchase #3	$98.83	5.592%	$104.3566	$104.36	$104.35	$104.40
Purchase #4	$101.58	11.840%	$113.6071	$113.61	$113.60	$113.60
Purchase #5	$113.95	10.629%	$126.0617	$126.06	$126.05	$126.10
Purchase #6	$146.52	12.556%	$164.9171	$164.92	$164.90	$164.90
Purchase #7	$72.67	13.751%	$82.6629	$82.66	$82.65	$82.70
7 purchase totals =	$821.77		$903.6826	$903.69	$903.65	$903.80