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	$55.86	7.195%	$59.8791	$59.88	$59.90	$59.90
Purchase #2	$136.57	10.761%	$151.2663	$151.27	$151.25	$151.30
Purchase #3	$33.35	11.115%	$37.0569	$37.06	$37.05	$37.10
Purchase #4	$202.34	6.266%	$215.0186	$215.02	$215.00	$215.00
Purchase #5	$86.47	9.751%	$94.9017	$94.90	$94.90	$94.90
Purchase #6	$52.26	11.190%	$58.1079	$58.11	$58.10	$58.10
Purchase #7	$22.82	9.356%	$24.955	$24.96	$24.95	$25.00
7 purchase totals =	$589.67		$641.1855	$641.20	$641.15	$641.30