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	$47.82	11.798%	$53.4618	$53.46	$53.45	$53.50
Purchase #2	$165.62	11.708%	$185.0108	$185.01	$185.00	$185.00
Purchase #3	$19.44	7.245%	$20.8484	$20.85	$20.85	$20.80
Purchase #4	$199.35	11.385%	$222.046	$222.05	$222.05	$222.00
Purchase #5	$148.84	7.235%	$159.6086	$159.61	$159.60	$159.60
Purchase #6	$154.44	5.490%	$162.9188	$162.92	$162.90	$162.90
Purchase #7	$28.48	8.785%	$30.982	$30.98	$31.00	$31.00
7 purchase totals =	$763.99		$834.8764	$834.88	$834.85	$834.80