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	$78.88	6.438%	$83.9583	$83.96	$83.95	$84.00
Purchase #2	$29.37	11.240%	$32.6712	$32.67	$32.65	$32.70
Purchase #3	$132.57	10.862%	$146.9698	$146.97	$146.95	$147.00
Purchase #4	$100.90	3.238%	$104.1671	$104.17	$104.15	$104.20
Purchase #5	$200.42	13.401%	$227.2783	$227.28	$227.30	$227.30
Purchase #6	$232.81	3.169%	$240.1877	$240.19	$240.20	$240.20
Purchase #7	$210.36	5.791%	$222.5419	$222.54	$222.55	$222.50
7 purchase totals =	$985.31		$1,057.7743	$1,057.78	$1,057.75	$1,057.90