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	$38.46	10.252%	$42.4029	$42.40	$42.40	$42.40
Purchase #2	$81.73	4.796%	$85.6498	$85.65	$85.65	$85.60
Purchase #3	$159.29	3.116%	$164.2535	$164.25	$164.25	$164.30
Purchase #4	$216.53	3.390%	$223.8704	$223.87	$223.85	$223.90
Purchase #5	$159.54	9.341%	$174.4426	$174.44	$174.45	$174.40
Purchase #6	$104.53	12.517%	$117.614	$117.61	$117.60	$117.60
Purchase #7	$66.98	6.179%	$71.1187	$71.12	$71.10	$71.10
7 purchase totals =	$827.06		$879.3519	$879.34	$879.30	$879.30