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	$76.41	5.102%	$80.3084	$80.31	$80.30	$80.30
Purchase #2	$61.64	6.527%	$65.6632	$65.66	$65.65	$65.70
Purchase #3	$84.92	5.740%	$89.7944	$89.79	$89.80	$89.80
Purchase #4	$81.78	4.409%	$85.3857	$85.39	$85.40	$85.40
Purchase #5	$183.54	13.649%	$208.5914	$208.59	$208.60	$208.60
Purchase #6	$113.37	6.269%	$120.4772	$120.48	$120.50	$120.50
Purchase #7	$229.40	10.872%	$254.3404	$254.34	$254.35	$254.30
7 purchase totals =	$831.06		$904.5607	$904.56	$904.60	$904.60