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	$37.36	4.681%	$39.1088	$39.11	$39.10	$39.10
Purchase #2	$50.86	7.688%	$54.7701	$54.77	$54.75	$54.80
Purchase #3	$60.34	12.424%	$67.8366	$67.84	$67.85	$67.80
Purchase #4	$81.47	5.441%	$85.9028	$85.90	$85.90	$85.90
Purchase #5	$92.37	9.368%	$101.0232	$101.02	$101.00	$101.00
Purchase #6	$154.74	9.334%	$169.1834	$169.18	$169.20	$169.20
Purchase #7	$59.78	12.786%	$67.4235	$67.42	$67.40	$67.40
7 purchase totals =	$536.92		$585.2484	$585.24	$585.20	$585.20