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	$190.73	4.794%	$199.8736	$199.87	$199.85	$199.90
Purchase #2	$114.50	13.459%	$129.9106	$129.91	$129.90	$129.90
Purchase #3	$73.70	4.484%	$77.0047	$77.00	$77.00	$77.00
Purchase #4	$131.89	11.437%	$146.9743	$146.97	$146.95	$147.00
Purchase #5	$32.85	4.596%	$34.3598	$34.36	$34.35	$34.40
Purchase #6	$130.30	10.715%	$144.2616	$144.26	$144.25	$144.30
Purchase #7	$53.38	11.273%	$59.3975	$59.40	$59.40	$59.40
7 purchase totals =	$727.35		$791.7821	$791.77	$791.70	$791.90