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	$37.77	4.837%	$39.5969	$39.60	$39.60	$39.60
Purchase #2	$136.97	4.568%	$143.2268	$143.23	$143.25	$143.20
Purchase #3	$193.69	3.198%	$199.8842	$199.88	$199.90	$199.90
Purchase #4	$233.36	5.375%	$245.9031	$245.90	$245.90	$245.90
Purchase #5	$214.68	12.842%	$242.2492	$242.25	$242.25	$242.20
Purchase #6	$80.57	11.155%	$89.5576	$89.56	$89.55	$89.60
Purchase #7	$57.83	13.332%	$65.5399	$65.54	$65.55	$65.50
7 purchase totals =	$954.87		$1,025.9577	$1,025.96	$1,026.00	$1,025.90