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	$168.46	13.306%	$190.8753	$190.88	$190.90	$190.90
Purchase #2	$125.62	13.325%	$142.3589	$142.36	$142.35	$142.40
Purchase #3	$192.48	8.542%	$208.9216	$208.92	$208.90	$208.90
Purchase #4	$75.82	13.154%	$85.7934	$85.79	$85.80	$85.80
Purchase #5	$41.33	3.770%	$42.8881	$42.89	$42.90	$42.90
Purchase #6	$230.91	4.210%	$240.6313	$240.63	$240.65	$240.60
Purchase #7	$176.37	7.384%	$189.3932	$189.39	$189.40	$189.40
7 purchase totals =	$1,010.99		$1,100.8618	$1,100.86	$1,100.90	$1,100.90