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	$78.94	11.585%	$88.0852	$88.09	$88.10	$88.10
Purchase #2	$228.89	6.494%	$243.7541	$243.75	$243.75	$243.80
Purchase #3	$49.54	7.638%	$53.3239	$53.32	$53.30	$53.30
Purchase #4	$100.51	8.681%	$109.2353	$109.24	$109.25	$109.20
Purchase #5	$93.50	11.205%	$103.9767	$103.98	$104.00	$104.00
Purchase #6	$18.83	11.648%	$21.0233	$21.02	$21.00	$21.00
Purchase #7	$199.59	4.652%	$208.8749	$208.87	$208.85	$208.90
7 purchase totals =	$769.80		$828.2734	$828.27	$828.25	$828.30