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	$250.80	13.581%	$284.8611	$284.86	$284.85	$284.90
Purchase #2	$35.57	12.690%	$40.0838	$40.08	$40.10	$40.10
Purchase #3	$239.62	4.712%	$250.9109	$250.91	$250.90	$250.90
Purchase #4	$17.72	9.838%	$19.4633	$19.46	$19.45	$19.50
Purchase #5	$26.76	8.439%	$29.0183	$29.02	$29.00	$29.00
Purchase #6	$52.82	12.860%	$59.6127	$59.61	$59.60	$59.60
Purchase #7	$242.50	9.120%	$264.616	$264.62	$264.60	$264.60
7 purchase totals =	$865.79		$948.5661	$948.56	$948.50	$948.60