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	$92.85	8.281%	$100.5389	$100.54	$100.55	$100.50
Purchase #2	$232.84	7.187%	$249.5742	$249.57	$249.55	$249.60
Purchase #3	$216.39	4.296%	$225.6861	$225.69	$225.70	$225.70
Purchase #4	$244.83	5.552%	$258.423	$258.42	$258.40	$258.40
Purchase #5	$140.25	13.533%	$159.23	$159.23	$159.25	$159.20
Purchase #6	$158.46	6.376%	$168.5634	$168.56	$168.55	$168.60
Purchase #7	$214.73	6.743%	$229.2092	$229.21	$229.20	$229.20
7 purchase totals =	$1,300.35		$1,391.2248	$1,391.22	$1,391.20	$1,391.20