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	$64.59	11.549%	$72.0495	$72.05	$72.05	$72.00
Purchase #2	$62.97	6.735%	$67.211	$67.21	$67.20	$67.20
Purchase #3	$53.80	9.160%	$58.7281	$58.73	$58.75	$58.70
Purchase #4	$223.76	6.558%	$238.4342	$238.43	$238.45	$238.40
Purchase #5	$79.89	6.419%	$85.0181	$85.02	$85.00	$85.00
Purchase #6	$102.74	10.290%	$113.3119	$113.31	$113.30	$113.30
Purchase #7	$55.85	9.783%	$61.3138	$61.31	$61.30	$61.30
7 purchase totals =	$643.60		$696.0666	$696.06	$696.05	$695.90