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	$81.35	12.218%	$91.2893	$91.29	$91.30	$91.30
Purchase #2	$86.88	5.610%	$91.754	$91.75	$91.75	$91.80
Purchase #3	$25.33	12.786%	$28.5687	$28.57	$28.55	$28.60
Purchase #4	$99.62	5.260%	$104.86	$104.86	$104.85	$104.90
Purchase #5	$50.89	9.167%	$55.5551	$55.56	$55.55	$55.60
Purchase #6	$199.59	9.603%	$218.7566	$218.76	$218.75	$218.80
Purchase #7	$80.31	9.852%	$88.2221	$88.22	$88.20	$88.20
7 purchase totals =	$623.97		$679.0058	$679.01	$678.95	$679.20