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	$198.89	6.790%	$212.3946	$212.39	$212.40	$212.40
Purchase #2	$238.45	9.249%	$260.5042	$260.50	$260.50	$260.50
Purchase #3	$209.97	12.801%	$236.8483	$236.85	$236.85	$236.80
Purchase #4	$51.73	11.400%	$57.6272	$57.63	$57.65	$57.60
Purchase #5	$36.82	11.133%	$40.9192	$40.92	$40.90	$40.90
Purchase #6	$81.77	7.742%	$88.1006	$88.10	$88.10	$88.10
Purchase #7	$99.78	6.739%	$106.5042	$106.50	$106.50	$106.50
7 purchase totals =	$917.41		$1,002.8983	$1,002.89	$1,002.90	$1,002.80