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	$80.26	7.799%	$86.5195	$86.52	$86.50	$86.50
Purchase #2	$90.57	3.427%	$93.6738	$93.67	$93.65	$93.70
Purchase #3	$208.33	12.539%	$234.4525	$234.45	$234.45	$234.50
Purchase #4	$88.41	11.731%	$98.7814	$98.78	$98.80	$98.80
Purchase #5	$61.69	5.231%	$64.917	$64.92	$64.90	$64.90
Purchase #6	$89.67	3.203%	$92.5421	$92.54	$92.55	$92.50
Purchase #7	$112.37	5.550%	$118.6065	$118.61	$118.60	$118.60
7 purchase totals =	$731.30		$789.4928	$789.49	$789.45	$789.50