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	$66.62	6.622%	$71.0316	$71.03	$71.05	$71.00
Purchase #2	$62.36	12.780%	$70.3296	$70.33	$70.35	$70.30
Purchase #3	$67.89	10.847%	$75.254	$75.25	$75.25	$75.30
Purchase #4	$59.28	8.864%	$64.5346	$64.53	$64.55	$64.50
Purchase #5	$165.38	9.339%	$180.8248	$180.82	$180.80	$180.80
Purchase #6	$234.94	6.361%	$249.8845	$249.88	$249.90	$249.90
Purchase #7	$76.38	12.501%	$85.9283	$85.93	$85.95	$85.90
7 purchase totals =	$732.85		$797.7874	$797.77	$797.85	$797.70