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	$31.89	13.512%	$36.199	$36.20	$36.20	$36.20
Purchase #2	$121.34	8.684%	$131.8772	$131.88	$131.90	$131.90
Purchase #3	$60.33	10.823%	$66.8595	$66.86	$66.85	$66.90
Purchase #4	$134.31	13.811%	$152.8596	$152.86	$152.85	$152.90
Purchase #5	$37.68	12.332%	$42.3267	$42.33	$42.35	$42.30
Purchase #6	$244.37	13.631%	$277.6801	$277.68	$277.70	$277.70
Purchase #7	$179.49	3.153%	$185.1493	$185.15	$185.15	$185.10
7 purchase totals =	$809.41		$892.9514	$892.96	$893.00	$893.00