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	$36.58	7.351%	$39.269	$39.27	$39.25	$39.30
Purchase #2	$77.32	10.110%	$85.1371	$85.14	$85.15	$85.10
Purchase #3	$244.38	10.801%	$270.7755	$270.78	$270.80	$270.80
Purchase #4	$113.77	9.821%	$124.9434	$124.94	$124.95	$124.90
Purchase #5	$208.61	13.569%	$236.9163	$236.92	$236.90	$236.90
Purchase #6	$55.57	11.816%	$62.1362	$62.14	$62.15	$62.10
Purchase #7	$98.65	13.666%	$112.1315	$112.13	$112.15	$112.10
7 purchase totals =	$834.88		$931.3090	$931.32	$931.35	$931.20