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	$218.57	11.374%	$243.4302	$243.43	$243.45	$243.40
Purchase #2	$214.89	10.230%	$236.8732	$236.87	$236.85	$236.90
Purchase #3	$124.82	10.213%	$137.5679	$137.57	$137.55	$137.60
Purchase #4	$65.92	9.807%	$72.3848	$72.38	$72.40	$72.40
Purchase #5	$96.28	7.223%	$103.2343	$103.23	$103.25	$103.20
Purchase #6	$40.68	8.462%	$44.1223	$44.12	$44.10	$44.10
Purchase #7	$131.92	7.104%	$141.2916	$141.29	$141.30	$141.30
7 purchase totals =	$893.08		$978.9043	$978.89	$978.90	$978.90