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	$156.83	3.378%	$162.1277	$162.13	$162.15	$162.10
Purchase #2	$78.94	8.197%	$85.4107	$85.41	$85.40	$85.40
Purchase #3	$227.53	9.850%	$249.9417	$249.94	$249.95	$249.90
Purchase #4	$82.92	11.514%	$92.4674	$92.47	$92.45	$92.50
Purchase #5	$46.80	7.774%	$50.4382	$50.44	$50.45	$50.40
Purchase #6	$184.77	11.562%	$206.1331	$206.13	$206.15	$206.10
Purchase #7	$10.27	10.669%	$11.3657	$11.37	$11.35	$11.40
7 purchase totals =	$788.06		$857.8845	$857.89	$857.90	$857.80