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	$7.51	10.874%	$8.3266	$8.33	$8.35	$8.30
Purchase #2	$32.89	12.360%	$36.9552	$36.96	$36.95	$37.00
Purchase #3	$250.27	10.366%	$276.213	$276.21	$276.20	$276.20
Purchase #4	$40.96	3.614%	$42.4403	$42.44	$42.45	$42.40
Purchase #5	$141.81	10.199%	$156.2732	$156.27	$156.25	$156.30
Purchase #6	$29.48	12.504%	$33.1662	$33.17	$33.15	$33.20
Purchase #7	$129.43	10.323%	$142.7911	$142.79	$142.80	$142.80
7 purchase totals =	$632.35		$696.1656	$696.17	$696.15	$696.20