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	$60.40	6.376%	$64.2511	$64.25	$64.25	$64.30
Purchase #2	$90.53	13.578%	$102.8222	$102.82	$102.80	$102.80
Purchase #3	$13.89	6.322%	$14.7681	$14.77	$14.75	$14.80
Purchase #4	$188.58	13.433%	$213.912	$213.91	$213.90	$213.90
Purchase #5	$43.77	3.435%	$45.2735	$45.27	$45.25	$45.30
Purchase #6	$144.80	11.383%	$161.2826	$161.28	$161.30	$161.30
Purchase #7	$191.49	3.682%	$198.5407	$198.54	$198.55	$198.50
7 purchase totals =	$733.46		$800.8502	$800.84	$800.80	$800.90