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	$115.80	12.543%	$130.3248	$130.32	$130.30	$130.30
Purchase #2	$37.89	13.140%	$42.8687	$42.87	$42.85	$42.90
Purchase #3	$119.80	5.503%	$126.3926	$126.39	$126.40	$126.40
Purchase #4	$236.88	12.248%	$265.8931	$265.89	$265.90	$265.90
Purchase #5	$162.37	7.752%	$174.9569	$174.96	$174.95	$175.00
Purchase #6	$106.41	9.782%	$116.819	$116.82	$116.80	$116.80
Purchase #7	$221.93	11.561%	$247.5873	$247.59	$247.60	$247.60
7 purchase totals =	$1,001.08		$1,104.8424	$1,104.84	$1,104.80	$1,104.90