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	$85.79	5.338%	$90.3695	$90.37	$90.35	$90.40
Purchase #2	$98.80	4.492%	$103.2381	$103.24	$103.25	$103.20
Purchase #3	$136.87	3.711%	$141.9492	$141.95	$141.95	$141.90
Purchase #4	$100.82	5.355%	$106.2189	$106.22	$106.20	$106.20
Purchase #5	$223.91	3.303%	$231.3057	$231.31	$231.30	$231.30
Purchase #6	$85.66	7.531%	$92.1111	$92.11	$92.10	$92.10
Purchase #7	$165.84	3.585%	$171.7854	$171.79	$171.80	$171.80
7 purchase totals =	$897.69		$936.9779	$936.99	$936.95	$936.90