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	$234.56	5.695%	$247.9182	$247.92	$247.90	$247.90
Purchase #2	$152.71	6.439%	$162.543	$162.54	$162.55	$162.50
Purchase #3	$63.61	4.514%	$66.4814	$66.48	$66.50	$66.50
Purchase #4	$43.58	4.798%	$45.671	$45.67	$45.65	$45.70
Purchase #5	$207.32	5.333%	$218.3764	$218.38	$218.40	$218.40
Purchase #6	$79.62	7.313%	$85.4426	$85.44	$85.45	$85.40
Purchase #7	$29.34	3.834%	$30.4649	$30.46	$30.45	$30.50
7 purchase totals =	$810.74		$856.8975	$856.89	$856.90	$856.90