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	$25.77	4.842%	$27.0178	$27.02	$27.00	$27.00
Purchase #2	$95.36	4.787%	$99.9249	$99.92	$99.90	$99.90
Purchase #3	$33.33	9.116%	$36.3684	$36.37	$36.35	$36.40
Purchase #4	$5.95	6.862%	$6.3583	$6.36	$6.35	$6.40
Purchase #5	$78.45	5.695%	$82.9177	$82.92	$82.90	$82.90
Purchase #6	$167.54	13.191%	$189.6402	$189.64	$189.65	$189.60
Purchase #7	$169.38	8.692%	$184.1025	$184.10	$184.10	$184.10
7 purchase totals =	$575.78		$626.3298	$626.33	$626.25	$626.30