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	$122.28	12.479%	$137.5393	$137.54	$137.55	$137.50
Purchase #2	$59.70	12.403%	$67.1046	$67.10	$67.10	$67.10
Purchase #3	$83.73	13.612%	$95.1273	$95.13	$95.15	$95.10
Purchase #4	$184.63	7.231%	$197.9806	$197.98	$198.00	$198.00
Purchase #5	$172.67	3.472%	$178.6651	$178.67	$178.65	$178.70
Purchase #6	$145.75	7.647%	$156.8955	$156.90	$156.90	$156.90
Purchase #7	$67.89	5.219%	$71.4332	$71.43	$71.45	$71.40
7 purchase totals =	$836.65		$904.7456	$904.75	$904.80	$904.70