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	$118.86	10.329%	$131.137	$131.14	$131.15	$131.10
Purchase #2	$136.50	5.254%	$143.6717	$143.67	$143.65	$143.70
Purchase #3	$73.93	6.215%	$78.5247	$78.52	$78.50	$78.50
Purchase #4	$239.73	10.295%	$264.4102	$264.41	$264.40	$264.40
Purchase #5	$76.98	11.477%	$85.815	$85.82	$85.80	$85.80
Purchase #6	$225.68	8.630%	$245.1562	$245.16	$245.15	$245.20
Purchase #7	$49.32	10.567%	$54.5316	$54.53	$54.55	$54.50
7 purchase totals =	$921.00		$1,003.2464	$1,003.25	$1,003.20	$1,003.20