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	$78.86	13.473%	$89.4848	$89.48	$89.50	$89.50
Purchase #2	$154.30	13.730%	$175.4854	$175.49	$175.50	$175.50
Purchase #3	$6.37	12.235%	$7.1494	$7.15	$7.15	$7.10
Purchase #4	$104.40	3.148%	$107.6865	$107.69	$107.70	$107.70
Purchase #5	$160.90	9.562%	$176.2853	$176.29	$176.30	$176.30
Purchase #6	$243.76	10.331%	$268.9428	$268.94	$268.95	$268.90
Purchase #7	$78.55	8.455%	$85.1914	$85.19	$85.20	$85.20
7 purchase totals =	$827.14		$910.2256	$910.23	$910.30	$910.20