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	$136.40	11.831%	$152.5375	$152.54	$152.55	$152.50
Purchase #2	$90.35	9.345%	$98.7932	$98.79	$98.80	$98.80
Purchase #3	$83.55	7.405%	$89.7369	$89.74	$89.75	$89.70
Purchase #4	$183.34	8.305%	$198.5664	$198.57	$198.55	$198.60
Purchase #5	$184.62	4.258%	$192.4811	$192.48	$192.50	$192.50
Purchase #6	$36.39	3.113%	$37.5228	$37.52	$37.50	$37.50
Purchase #7	$188.97	6.681%	$201.5951	$201.60	$201.60	$201.60
7 purchase totals =	$903.62		$971.2330	$971.24	$971.25	$971.20