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	$29.37	9.474%	$32.1525	$32.15	$32.15	$32.20
Purchase #2	$176.95	3.215%	$182.6389	$182.64	$182.65	$182.60
Purchase #3	$134.90	11.441%	$150.3339	$150.33	$150.35	$150.30
Purchase #4	$64.54	5.119%	$67.8438	$67.84	$67.85	$67.80
Purchase #5	$222.65	13.552%	$252.8235	$252.82	$252.80	$252.80
Purchase #6	$174.35	11.578%	$194.5362	$194.54	$194.55	$194.50
Purchase #7	$142.96	3.615%	$148.128	$148.13	$148.15	$148.10
7 purchase totals =	$945.72		$1,028.4568	$1,028.45	$1,028.50	$1,028.30