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	$11.83	7.299%	$12.6935	$12.69	$12.70	$12.70
Purchase #2	$52.33	4.171%	$54.5127	$54.51	$54.50	$54.50
Purchase #3	$198.31	11.408%	$220.9332	$220.93	$220.95	$220.90
Purchase #4	$68.28	5.798%	$72.2389	$72.24	$72.25	$72.20
Purchase #5	$82.26	9.668%	$90.2129	$90.21	$90.20	$90.20
Purchase #6	$213.64	4.566%	$223.3948	$223.39	$223.40	$223.40
Purchase #7	$198.44	7.802%	$213.9223	$213.92	$213.90	$213.90
7 purchase totals =	$825.09		$887.9083	$887.89	$887.90	$887.80