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	$243.55	8.702%	$264.7437	$264.74	$264.75	$264.70
Purchase #2	$54.53	13.299%	$61.7819	$61.78	$61.80	$61.80
Purchase #3	$136.44	3.273%	$140.9057	$140.91	$140.90	$140.90
Purchase #4	$129.83	13.512%	$147.3726	$147.37	$147.35	$147.40
Purchase #5	$87.90	4.210%	$91.6006	$91.60	$91.60	$91.60
Purchase #6	$44.83	11.791%	$50.1159	$50.12	$50.10	$50.10
Purchase #7	$82.34	8.549%	$89.3792	$89.38	$89.40	$89.40
7 purchase totals =	$779.42		$845.8996	$845.90	$845.90	$845.90