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	$150.37	4.284%	$156.8119	$156.81	$156.80	$156.80
Purchase #2	$210.29	3.774%	$218.2263	$218.23	$218.25	$218.20
Purchase #3	$234.34	3.406%	$242.3216	$242.32	$242.30	$242.30
Purchase #4	$5.98	7.279%	$6.4153	$6.42	$6.40	$6.40
Purchase #5	$30.27	8.780%	$32.9277	$32.93	$32.95	$32.90
Purchase #6	$91.78	8.619%	$99.6905	$99.69	$99.70	$99.70
Purchase #7	$7.89	12.730%	$8.8944	$8.89	$8.90	$8.90
7 purchase totals =	$730.92		$765.2877	$765.29	$765.30	$765.20