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	$172.82	12.701%	$194.7699	$194.77	$194.75	$194.80
Purchase #2	$91.26	6.156%	$96.878	$96.88	$96.90	$96.90
Purchase #3	$61.70	3.788%	$64.0372	$64.04	$64.05	$64.00
Purchase #4	$182.41	9.418%	$199.5894	$199.59	$199.60	$199.60
Purchase #5	$108.48	10.598%	$119.9767	$119.98	$120.00	$120.00
Purchase #6	$80.46	11.462%	$89.6823	$89.68	$89.70	$89.70
Purchase #7	$94.61	11.858%	$105.8289	$105.83	$105.85	$105.80
7 purchase totals =	$791.74		$870.7624	$870.77	$870.85	$870.80