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	$83.58	7.190%	$89.5894	$89.59	$89.60	$89.60
Purchase #2	$130.47	6.464%	$138.9036	$138.90	$138.90	$138.90
Purchase #3	$234.65	11.737%	$262.1909	$262.19	$262.20	$262.20
Purchase #4	$31.26	3.231%	$32.27	$32.27	$32.25	$32.30
Purchase #5	$159.50	6.740%	$170.2503	$170.25	$170.25	$170.30
Purchase #6	$82.79	9.700%	$90.8206	$90.82	$90.80	$90.80
Purchase #7	$244.85	3.413%	$253.2067	$253.21	$253.20	$253.20
7 purchase totals =	$967.10		$1,037.2315	$1,037.23	$1,037.20	$1,037.30