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	$113.46	4.423%	$118.4783	$118.48	$118.50	$118.50
Purchase #2	$115.98	9.643%	$127.164	$127.16	$127.15	$127.20
Purchase #3	$72.42	13.192%	$81.9736	$81.97	$81.95	$82.00
Purchase #4	$196.63	4.404%	$205.2896	$205.29	$205.30	$205.30
Purchase #5	$83.33	11.402%	$92.8313	$92.83	$92.85	$92.80
Purchase #6	$97.25	12.460%	$109.3674	$109.37	$109.35	$109.40
Purchase #7	$195.47	5.741%	$206.6919	$206.69	$206.70	$206.70
7 purchase totals =	$874.54		$941.7961	$941.79	$941.80	$941.90