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	$102.96	6.280%	$109.4259	$109.43	$109.45	$109.40
Purchase #2	$128.69	12.512%	$144.7917	$144.79	$144.80	$144.80
Purchase #3	$29.97	9.738%	$32.8885	$32.89	$32.90	$32.90
Purchase #4	$83.70	13.833%	$95.2782	$95.28	$95.30	$95.30
Purchase #5	$165.92	12.274%	$186.285	$186.29	$186.30	$186.30
Purchase #6	$97.64	7.106%	$104.5783	$104.58	$104.60	$104.60
Purchase #7	$88.82	8.713%	$96.5589	$96.56	$96.55	$96.60
7 purchase totals =	$697.70		$769.8065	$769.82	$769.90	$769.90