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	$120.57	6.143%	$127.9766	$127.98	$128.00	$128.00
Purchase #2	$124.33	13.283%	$140.8448	$140.84	$140.85	$140.80
Purchase #3	$18.93	8.364%	$20.5133	$20.51	$20.50	$20.50
Purchase #4	$202.29	13.396%	$229.3888	$229.39	$229.40	$229.40
Purchase #5	$210.30	5.352%	$221.5553	$221.56	$221.55	$221.60
Purchase #6	$140.31	8.419%	$152.1227	$152.12	$152.10	$152.10
Purchase #7	$93.56	12.189%	$104.964	$104.96	$104.95	$105.00
7 purchase totals =	$910.29		$997.3655	$997.36	$997.35	$997.40