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	$40.99	4.311%	$42.7571	$42.76	$42.75	$42.80
Purchase #2	$55.42	11.102%	$61.5727	$61.57	$61.55	$61.60
Purchase #3	$219.79	13.728%	$249.9628	$249.96	$249.95	$250.00
Purchase #4	$207.69	9.650%	$227.7321	$227.73	$227.75	$227.70
Purchase #5	$164.49	10.871%	$182.3717	$182.37	$182.35	$182.40
Purchase #6	$200.90	4.774%	$210.491	$210.49	$210.50	$210.50
Purchase #7	$110.54	5.149%	$116.2317	$116.23	$116.25	$116.20
7 purchase totals =	$999.82		$1,091.1191	$1,091.11	$1,091.10	$1,091.20