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	$43.37	5.869%	$45.9154	$45.92	$45.90	$45.90
Purchase #2	$142.90	11.728%	$159.6593	$159.66	$159.65	$159.70
Purchase #3	$210.72	4.595%	$220.4026	$220.40	$220.40	$220.40
Purchase #4	$189.98	7.811%	$204.8193	$204.82	$204.80	$204.80
Purchase #5	$167.71	6.449%	$178.5256	$178.53	$178.55	$178.50
Purchase #6	$19.72	10.145%	$21.7206	$21.72	$21.70	$21.70
Purchase #7	$148.84	13.334%	$168.6863	$168.69	$168.70	$168.70
7 purchase totals =	$923.24		$999.7291	$999.74	$999.70	$999.70