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	$66.69	8.750%	$72.5254	$72.53	$72.55	$72.50
Purchase #2	$234.60	12.588%	$264.1314	$264.13	$264.15	$264.10
Purchase #3	$82.80	9.408%	$90.5898	$90.59	$90.60	$90.60
Purchase #4	$31.64	5.420%	$33.3549	$33.35	$33.35	$33.40
Purchase #5	$78.41	9.535%	$85.8864	$85.89	$85.90	$85.90
Purchase #6	$66.64	6.673%	$71.0869	$71.09	$71.10	$71.10
Purchase #7	$67.78	12.386%	$76.1752	$76.18	$76.20	$76.20
7 purchase totals =	$628.56		$693.7500	$693.76	$693.85	$693.80