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	$198.76	13.291%	$225.1772	$225.18	$225.20	$225.20
Purchase #2	$81.65	6.236%	$86.7417	$86.74	$86.75	$86.70
Purchase #3	$39.56	4.329%	$41.2726	$41.27	$41.25	$41.30
Purchase #4	$185.42	12.257%	$208.1469	$208.15	$208.15	$208.10
Purchase #5	$250.95	7.328%	$269.3396	$269.34	$269.35	$269.30
Purchase #6	$82.89	12.844%	$93.5364	$93.54	$93.55	$93.50
Purchase #7	$78.97	11.773%	$88.2671	$88.27	$88.25	$88.30
7 purchase totals =	$918.20		$1,012.4815	$1,012.49	$1,012.50	$1,012.40