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	$189.77	10.777%	$210.2215	$210.22	$210.20	$210.20
Purchase #2	$209.42	6.378%	$222.7768	$222.78	$222.80	$222.80
Purchase #3	$84.82	6.669%	$90.4766	$90.48	$90.50	$90.50
Purchase #4	$210.50	3.744%	$218.3811	$218.38	$218.40	$218.40
Purchase #5	$7.31	7.209%	$7.837	$7.84	$7.85	$7.80
Purchase #6	$80.68	10.486%	$89.1401	$89.14	$89.15	$89.10
Purchase #7	$33.72	11.581%	$37.6251	$37.63	$37.65	$37.60
7 purchase totals =	$816.22		$876.4582	$876.47	$876.55	$876.40