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	$90.33	13.716%	$102.7197	$102.72	$102.70	$102.70
Purchase #2	$129.48	4.198%	$134.9156	$134.92	$134.90	$134.90
Purchase #3	$31.98	11.124%	$35.5375	$35.54	$35.55	$35.50
Purchase #4	$85.41	5.400%	$90.0221	$90.02	$90.00	$90.00
Purchase #5	$207.61	7.652%	$223.4963	$223.50	$223.50	$223.50
Purchase #6	$45.38	8.298%	$49.1456	$49.15	$49.15	$49.10
Purchase #7	$70.32	3.165%	$72.5456	$72.55	$72.55	$72.50
7 purchase totals =	$660.51		$708.3824	$708.40	$708.35	$708.20