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	$165.71	3.519%	$171.5413	$171.54	$171.55	$171.50
Purchase #2	$85.39	5.445%	$90.0395	$90.04	$90.05	$90.00
Purchase #3	$113.38	3.227%	$117.0388	$117.04	$117.05	$117.00
Purchase #4	$87.72	3.491%	$90.7823	$90.78	$90.80	$90.80
Purchase #5	$168.82	13.350%	$191.3575	$191.36	$191.35	$191.40
Purchase #6	$226.68	8.235%	$245.3471	$245.35	$245.35	$245.30
Purchase #7	$98.79	10.477%	$109.1402	$109.14	$109.15	$109.10
7 purchase totals =	$946.49		$1,015.2467	$1,015.25	$1,015.30	$1,015.10