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	$54.88	8.381%	$59.4795	$59.48	$59.50	$59.50
Purchase #2	$204.28	13.871%	$232.6157	$232.62	$232.60	$232.60
Purchase #3	$219.77	11.837%	$245.7842	$245.78	$245.80	$245.80
Purchase #4	$155.75	8.731%	$169.3485	$169.35	$169.35	$169.30
Purchase #5	$136.70	3.585%	$141.6007	$141.60	$141.60	$141.60
Purchase #6	$149.51	4.502%	$156.2409	$156.24	$156.25	$156.20
Purchase #7	$43.53	3.432%	$45.0239	$45.02	$45.00	$45.00
7 purchase totals =	$964.42		$1,050.0934	$1,050.09	$1,050.10	$1,050.00