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	$233.89	10.437%	$258.3011	$258.30	$258.30	$258.30
Purchase #2	$140.57	8.870%	$153.0386	$153.04	$153.05	$153.00
Purchase #3	$134.70	4.687%	$141.0134	$141.01	$141.00	$141.00
Purchase #4	$201.96	11.589%	$225.3651	$225.37	$225.35	$225.40
Purchase #5	$121.82	12.615%	$137.1876	$137.19	$137.20	$137.20
Purchase #6	$79.62	12.761%	$89.7803	$89.78	$89.80	$89.80
Purchase #7	$179.98	9.412%	$196.9197	$196.92	$196.90	$196.90
7 purchase totals =	$1,092.54		$1,201.6058	$1,201.61	$1,201.60	$1,201.60