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	$238.45	13.328%	$270.2306	$270.23	$270.25	$270.20
Purchase #2	$175.37	7.805%	$189.0576	$189.06	$189.05	$189.10
Purchase #3	$103.27	6.348%	$109.8256	$109.83	$109.85	$109.80
Purchase #4	$130.86	6.408%	$139.2455	$139.25	$139.25	$139.20
Purchase #5	$67.80	3.464%	$70.1486	$70.15	$70.15	$70.10
Purchase #6	$7.61	3.635%	$7.8866	$7.89	$7.90	$7.90
Purchase #7	$250.82	5.605%	$264.8785	$264.88	$264.90	$264.90
7 purchase totals =	$974.18		$1,051.2730	$1,051.29	$1,051.35	$1,051.20