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	$96.69	6.313%	$102.794	$102.79	$102.80	$102.80
Purchase #2	$127.89	12.499%	$143.875	$143.88	$143.90	$143.90
Purchase #3	$91.29	9.360%	$99.8347	$99.83	$99.85	$99.80
Purchase #4	$135.35	4.264%	$141.1213	$141.12	$141.10	$141.10
Purchase #5	$232.80	3.258%	$240.3846	$240.38	$240.40	$240.40
Purchase #6	$203.61	12.439%	$228.937	$228.94	$228.95	$228.90
Purchase #7	$75.40	13.139%	$85.3068	$85.31	$85.30	$85.30
7 purchase totals =	$963.03		$1,042.2534	$1,042.25	$1,042.30	$1,042.20