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	$238.56	8.118%	$257.9263	$257.93	$257.95	$257.90
Purchase #2	$67.59	5.490%	$71.3007	$71.30	$71.30	$71.30
Purchase #3	$237.79	4.132%	$247.6155	$247.62	$247.60	$247.60
Purchase #4	$157.47	3.312%	$162.6854	$162.69	$162.70	$162.70
Purchase #5	$106.30	4.766%	$111.3663	$111.37	$111.35	$111.40
Purchase #6	$147.69	12.402%	$166.0065	$166.01	$166.00	$166.00
Purchase #7	$30.96	3.310%	$31.9848	$31.98	$32.00	$32.00
7 purchase totals =	$986.36		$1,048.8855	$1,048.90	$1,048.90	$1,048.90