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	$35.55	10.642%	$39.3332	$39.33	$39.35	$39.30
Purchase #2	$200.35	4.404%	$209.1734	$209.17	$209.15	$209.20
Purchase #3	$103.33	10.631%	$114.315	$114.32	$114.30	$114.30
Purchase #4	$189.43	5.590%	$200.0191	$200.02	$200.00	$200.00
Purchase #5	$131.88	10.314%	$145.4821	$145.48	$145.50	$145.50
Purchase #6	$16.61	9.714%	$18.2235	$18.22	$18.20	$18.20
Purchase #7	$156.57	7.568%	$168.4192	$168.42	$168.40	$168.40
7 purchase totals =	$833.72		$894.9655	$894.96	$894.90	$894.90