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	$36.86	9.410%	$40.3285	$40.33	$40.35	$40.30
Purchase #2	$128.93	13.424%	$146.2376	$146.24	$146.25	$146.20
Purchase #3	$87.33	12.845%	$98.5475	$98.55	$98.55	$98.50
Purchase #4	$118.98	9.614%	$130.4187	$130.42	$130.40	$130.40
Purchase #5	$37.62	8.778%	$40.9223	$40.92	$40.90	$40.90
Purchase #6	$158.44	7.506%	$170.3325	$170.33	$170.35	$170.30
Purchase #7	$63.45	6.290%	$67.441	$67.44	$67.45	$67.40
7 purchase totals =	$631.61		$694.2281	$694.23	$694.25	$694.00