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	$221.50	5.667%	$234.0524	$234.05	$234.05	$234.10
Purchase #2	$116.68	12.363%	$131.1051	$131.11	$131.10	$131.10
Purchase #3	$225.89	7.503%	$242.8385	$242.84	$242.85	$242.80
Purchase #4	$27.56	12.646%	$31.0452	$31.05	$31.05	$31.00
Purchase #5	$226.39	7.284%	$242.8802	$242.88	$242.90	$242.90
Purchase #6	$242.95	11.449%	$270.7653	$270.77	$270.75	$270.80
Purchase #7	$219.48	13.518%	$249.1493	$249.15	$249.15	$249.10
7 purchase totals =	$1,280.45		$1,401.8360	$1,401.85	$1,401.85	$1,401.80