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	$130.57	6.570%	$139.1484	$139.15	$139.15	$139.10
Purchase #2	$185.90	12.253%	$208.6783	$208.68	$208.70	$208.70
Purchase #3	$159.96	7.439%	$171.8594	$171.86	$171.85	$171.90
Purchase #4	$126.73	4.802%	$132.8156	$132.82	$132.80	$132.80
Purchase #5	$52.58	12.205%	$58.9974	$59.00	$59.00	$59.00
Purchase #6	$88.59	10.435%	$97.8344	$97.83	$97.85	$97.80
Purchase #7	$229.65	8.801%	$249.8615	$249.86	$249.85	$249.90
7 purchase totals =	$973.98		$1,059.1950	$1,059.20	$1,059.20	$1,059.20