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	$110.48	6.337%	$117.4811	$117.48	$117.50	$117.50
Purchase #2	$65.36	11.412%	$72.8189	$72.82	$72.80	$72.80
Purchase #3	$37.58	8.183%	$40.6552	$40.66	$40.65	$40.70
Purchase #4	$65.91	10.473%	$72.8128	$72.81	$72.80	$72.80
Purchase #5	$162.63	12.454%	$182.8839	$182.88	$182.90	$182.90
Purchase #6	$49.98	13.854%	$56.9042	$56.90	$56.90	$56.90
Purchase #7	$206.71	4.868%	$216.7726	$216.77	$216.75	$216.80
7 purchase totals =	$698.65		$760.3287	$760.32	$760.30	$760.40