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	$215.25	8.386%	$233.3009	$233.30	$233.30	$233.30
Purchase #2	$77.26	11.173%	$85.8923	$85.89	$85.90	$85.90
Purchase #3	$152.57	11.775%	$170.5351	$170.54	$170.55	$170.50
Purchase #4	$86.85	4.225%	$90.5194	$90.52	$90.50	$90.50
Purchase #5	$78.46	10.713%	$86.8654	$86.87	$86.85	$86.90
Purchase #6	$140.64	6.265%	$149.4511	$149.45	$149.45	$149.50
Purchase #7	$225.89	6.825%	$241.307	$241.31	$241.30	$241.30
7 purchase totals =	$976.92		$1,057.8712	$1,057.88	$1,057.85	$1,057.90