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	$80.73	12.254%	$90.6227	$90.62	$90.60	$90.60
Purchase #2	$214.74	11.764%	$240.002	$240.00	$240.00	$240.00
Purchase #3	$145.73	4.713%	$152.5983	$152.60	$152.60	$152.60
Purchase #4	$110.33	13.518%	$125.2444	$125.24	$125.25	$125.20
Purchase #5	$198.65	12.378%	$223.2389	$223.24	$223.25	$223.20
Purchase #6	$78.37	3.206%	$80.8825	$80.88	$80.90	$80.90
Purchase #7	$50.48	3.445%	$52.219	$52.22	$52.20	$52.20
7 purchase totals =	$879.03		$964.8078	$964.80	$964.80	$964.70