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	$110.75	11.314%	$123.2803	$123.28	$123.30	$123.30
Purchase #2	$211.57	4.550%	$221.1964	$221.20	$221.20	$221.20
Purchase #3	$189.96	12.520%	$213.743	$213.74	$213.75	$213.70
Purchase #4	$68.70	5.256%	$72.3109	$72.31	$72.30	$72.30
Purchase #5	$157.76	8.765%	$171.5877	$171.59	$171.60	$171.60
Purchase #6	$103.93	4.165%	$108.2587	$108.26	$108.25	$108.30
Purchase #7	$76.90	7.656%	$82.7875	$82.79	$82.80	$82.80
7 purchase totals =	$919.57		$993.1645	$993.17	$993.20	$993.20