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	$240.47	6.867%	$256.9831	$256.98	$257.00	$257.00
Purchase #2	$89.41	6.865%	$95.548	$95.55	$95.55	$95.50
Purchase #3	$213.93	10.375%	$236.1252	$236.13	$236.15	$236.10
Purchase #4	$221.36	9.381%	$242.1258	$242.13	$242.15	$242.10
Purchase #5	$156.46	7.670%	$168.4605	$168.46	$168.45	$168.50
Purchase #6	$79.82	12.620%	$89.8933	$89.89	$89.90	$89.90
Purchase #7	$88.92	11.392%	$99.0498	$99.05	$99.05	$99.00
7 purchase totals =	$1,090.37		$1,188.1857	$1,188.19	$1,188.25	$1,188.10