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	$32.68	3.753%	$33.9065	$33.91	$33.90	$33.90
Purchase #2	$84.59	3.457%	$87.5143	$87.51	$87.50	$87.50
Purchase #3	$109.94	7.605%	$118.3009	$118.30	$118.30	$118.30
Purchase #4	$53.29	12.244%	$59.8148	$59.81	$59.80	$59.80
Purchase #5	$163.64	8.628%	$177.7589	$177.76	$177.75	$177.80
Purchase #6	$183.27	7.432%	$196.8906	$196.89	$196.90	$196.90
Purchase #7	$206.85	13.356%	$234.4769	$234.48	$234.50	$234.50
7 purchase totals =	$834.26		$908.6629	$908.66	$908.65	$908.70