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	$18.50	11.311%	$20.5925	$20.59	$20.60	$20.60
Purchase #2	$88.73	10.629%	$98.1611	$98.16	$98.15	$98.20
Purchase #3	$171.83	11.473%	$191.5441	$191.54	$191.55	$191.50
Purchase #4	$42.25	13.378%	$47.9022	$47.90	$47.90	$47.90
Purchase #5	$221.43	12.303%	$248.6725	$248.67	$248.65	$248.70
Purchase #6	$88.81	8.392%	$96.2629	$96.26	$96.25	$96.30
Purchase #7	$60.96	3.818%	$63.2875	$63.29	$63.30	$63.30
7 purchase totals =	$692.51		$766.4228	$766.41	$766.40	$766.50