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	$28.46	11.823%	$31.8248	$31.82	$31.80	$31.80
Purchase #2	$221.57	10.519%	$244.8769	$244.88	$244.90	$244.90
Purchase #3	$151.36	3.228%	$156.2459	$156.25	$156.25	$156.20
Purchase #4	$82.80	10.291%	$91.3209	$91.32	$91.30	$91.30
Purchase #5	$232.90	4.291%	$242.8937	$242.89	$242.90	$242.90
Purchase #6	$50.29	12.426%	$56.539	$56.54	$56.55	$56.50
Purchase #7	$110.65	9.293%	$120.9327	$120.93	$120.95	$120.90
7 purchase totals =	$878.03		$944.6339	$944.63	$944.65	$944.50