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	$215.82	12.688%	$243.2032	$243.20	$243.20	$243.20
Purchase #2	$175.32	13.427%	$198.8602	$198.86	$198.85	$198.90
Purchase #3	$215.98	11.456%	$240.7227	$240.72	$240.70	$240.70
Purchase #4	$128.29	6.106%	$136.1234	$136.12	$136.10	$136.10
Purchase #5	$146.50	13.160%	$165.7794	$165.78	$165.80	$165.80
Purchase #6	$63.96	11.276%	$71.1721	$71.17	$71.15	$71.20
Purchase #7	$7.93	7.110%	$8.4938	$8.49	$8.50	$8.50
7 purchase totals =	$953.80		$1,064.3548	$1,064.34	$1,064.30	$1,064.40