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	$139.69	12.701%	$157.432	$157.43	$157.45	$157.40
Purchase #2	$250.48	7.436%	$269.1057	$269.11	$269.10	$269.10
Purchase #3	$95.84	3.586%	$99.2768	$99.28	$99.30	$99.30
Purchase #4	$108.73	13.401%	$123.3009	$123.30	$123.30	$123.30
Purchase #5	$84.66	8.593%	$91.9348	$91.93	$91.95	$91.90
Purchase #6	$91.66	10.293%	$101.0946	$101.09	$101.10	$101.10
Purchase #7	$86.31	5.165%	$90.7679	$90.77	$90.75	$90.80
7 purchase totals =	$857.37		$932.9127	$932.91	$932.95	$932.90