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	$65.55	12.138%	$73.5065	$73.51	$73.50	$73.50
Purchase #2	$155.68	7.148%	$166.808	$166.81	$166.80	$166.80
Purchase #3	$82.73	9.729%	$90.7788	$90.78	$90.80	$90.80
Purchase #4	$123.67	11.507%	$137.9007	$137.90	$137.90	$137.90
Purchase #5	$126.86	8.102%	$137.1382	$137.14	$137.15	$137.10
Purchase #6	$227.67	10.424%	$251.4023	$251.40	$251.40	$251.40
Purchase #7	$136.52	8.203%	$147.7187	$147.72	$147.70	$147.70
7 purchase totals =	$918.68		$1,005.2532	$1,005.26	$1,005.25	$1,005.20