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	$229.36	11.590%	$255.9428	$255.94	$255.95	$255.90
Purchase #2	$77.36	7.585%	$83.2278	$83.23	$83.25	$83.20
Purchase #3	$86.89	3.249%	$89.7131	$89.71	$89.70	$89.70
Purchase #4	$180.31	8.331%	$195.3316	$195.33	$195.35	$195.30
Purchase #5	$17.69	13.864%	$20.1425	$20.14	$20.15	$20.10
Purchase #6	$96.85	7.350%	$103.9685	$103.97	$103.95	$104.00
Purchase #7	$141.31	5.614%	$149.2431	$149.24	$149.25	$149.20
7 purchase totals =	$829.77		$897.5694	$897.56	$897.60	$897.40