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	$20.60	8.432%	$22.337	$22.34	$22.35	$22.30
Purchase #2	$131.86	4.368%	$137.6196	$137.62	$137.60	$137.60
Purchase #3	$55.50	6.719%	$59.229	$59.23	$59.25	$59.20
Purchase #4	$243.80	12.721%	$274.8138	$274.81	$274.80	$274.80
Purchase #5	$102.86	6.424%	$109.4677	$109.47	$109.45	$109.50
Purchase #6	$165.35	8.319%	$179.1055	$179.11	$179.10	$179.10
Purchase #7	$114.27	5.703%	$120.7868	$120.79	$120.80	$120.80
7 purchase totals =	$834.24		$903.3594	$903.37	$903.35	$903.30