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	$112.85	7.171%	$120.9425	$120.94	$120.95	$120.90
Purchase #2	$73.57	7.465%	$79.062	$79.06	$79.05	$79.10
Purchase #3	$99.78	12.699%	$112.4511	$112.45	$112.45	$112.50
Purchase #4	$135.31	4.417%	$141.2866	$141.29	$141.30	$141.30
Purchase #5	$95.47	3.267%	$98.589	$98.59	$98.60	$98.60
Purchase #6	$35.61	9.133%	$38.8623	$38.86	$38.85	$38.90
Purchase #7	$56.74	4.603%	$59.3517	$59.35	$59.35	$59.40
7 purchase totals =	$609.33		$650.5452	$650.54	$650.55	$650.70