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	$160.86	9.861%	$176.7224	$176.72	$176.70	$176.70
Purchase #2	$6.98	13.142%	$7.8973	$7.90	$7.90	$7.90
Purchase #3	$183.82	5.552%	$194.0257	$194.03	$194.05	$194.00
Purchase #4	$225.61	8.842%	$245.5584	$245.56	$245.55	$245.60
Purchase #5	$191.44	12.362%	$215.1058	$215.11	$215.10	$215.10
Purchase #6	$50.75	6.300%	$53.9473	$53.95	$53.95	$53.90
Purchase #7	$83.94	7.167%	$89.956	$89.96	$89.95	$90.00
7 purchase totals =	$903.40		$983.2129	$983.23	$983.20	$983.20