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	$71.71	13.361%	$81.2912	$81.29	$81.30	$81.30
Purchase #2	$109.40	9.130%	$119.3882	$119.39	$119.40	$119.40
Purchase #3	$112.86	9.437%	$123.5106	$123.51	$123.50	$123.50
Purchase #4	$145.30	7.581%	$156.3152	$156.32	$156.30	$156.30
Purchase #5	$195.62	11.218%	$217.5647	$217.56	$217.55	$217.60
Purchase #6	$71.43	11.872%	$79.9102	$79.91	$79.90	$79.90
Purchase #7	$241.51	3.320%	$249.5281	$249.53	$249.55	$249.50
7 purchase totals =	$947.83		$1,027.5082	$1,027.51	$1,027.50	$1,027.50