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	$110.72	11.620%	$123.5857	$123.59	$123.60	$123.60
Purchase #2	$241.41	11.214%	$268.4817	$268.48	$268.50	$268.50
Purchase #3	$189.70	9.284%	$207.3117	$207.31	$207.30	$207.30
Purchase #4	$48.29	8.676%	$52.4796	$52.48	$52.50	$52.50
Purchase #5	$47.43	3.116%	$48.9079	$48.91	$48.90	$48.90
Purchase #6	$131.64	7.731%	$141.8171	$141.82	$141.80	$141.80
Purchase #7	$111.31	11.600%	$124.222	$124.22	$124.20	$124.20
7 purchase totals =	$880.50		$966.8057	$966.81	$966.80	$966.80