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	$19.33	10.595%	$21.378	$21.38	$21.40	$21.40
Purchase #2	$64.63	8.556%	$70.1597	$70.16	$70.15	$70.20
Purchase #3	$234.59	10.110%	$258.307	$258.31	$258.30	$258.30
Purchase #4	$195.89	8.577%	$212.6915	$212.69	$212.70	$212.70
Purchase #5	$228.31	11.218%	$253.9218	$253.92	$253.90	$253.90
Purchase #6	$73.55	12.661%	$82.8622	$82.86	$82.85	$82.90
Purchase #7	$29.38	10.865%	$32.5721	$32.57	$32.55	$32.60
7 purchase totals =	$845.68		$931.8923	$931.89	$931.85	$932.00