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	$178.61	4.321%	$186.3277	$186.33	$186.35	$186.30
Purchase #2	$231.56	7.554%	$249.052	$249.05	$249.05	$249.10
Purchase #3	$148.53	7.580%	$159.7886	$159.79	$159.80	$159.80
Purchase #4	$82.48	7.347%	$88.5398	$88.54	$88.55	$88.50
Purchase #5	$67.89	5.860%	$71.8684	$71.87	$71.85	$71.90
Purchase #6	$240.32	6.703%	$256.4286	$256.43	$256.45	$256.40
Purchase #7	$24.55	13.496%	$27.8633	$27.86	$27.85	$27.90
7 purchase totals =	$973.94		$1,039.8684	$1,039.87	$1,039.90	$1,039.90