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	$81.36	10.504%	$89.9061	$89.91	$89.90	$89.90
Purchase #2	$52.97	12.441%	$59.56	$59.56	$59.55	$59.60
Purchase #3	$188.75	11.582%	$210.611	$210.61	$210.60	$210.60
Purchase #4	$95.30	6.438%	$101.4354	$101.44	$101.45	$101.40
Purchase #5	$140.77	7.296%	$151.0406	$151.04	$151.05	$151.00
Purchase #6	$12.78	12.652%	$14.3969	$14.40	$14.40	$14.40
Purchase #7	$223.64	9.736%	$245.4136	$245.41	$245.40	$245.40
7 purchase totals =	$795.57		$872.3636	$872.37	$872.35	$872.30