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	$170.84	11.707%	$190.8402	$190.84	$190.85	$190.80
Purchase #2	$144.68	12.515%	$162.7867	$162.79	$162.80	$162.80
Purchase #3	$163.73	13.616%	$186.0235	$186.02	$186.00	$186.00
Purchase #4	$94.47	6.279%	$100.4018	$100.40	$100.40	$100.40
Purchase #5	$237.78	11.132%	$264.2497	$264.25	$264.25	$264.20
Purchase #6	$52.89	6.462%	$56.3078	$56.31	$56.30	$56.30
Purchase #7	$90.99	6.871%	$97.2419	$97.24	$97.25	$97.20
7 purchase totals =	$955.38		$1,057.8516	$1,057.85	$1,057.85	$1,057.70