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	$237.35	5.671%	$250.8101	$250.81	$250.80	$250.80
Purchase #2	$222.56	9.526%	$243.7611	$243.76	$243.75	$243.80
Purchase #3	$85.76	4.181%	$89.3456	$89.35	$89.35	$89.30
Purchase #4	$88.76	10.569%	$98.141	$98.14	$98.15	$98.10
Purchase #5	$227.83	4.507%	$238.0983	$238.10	$238.10	$238.10
Purchase #6	$121.98	12.110%	$136.7518	$136.75	$136.75	$136.80
Purchase #7	$204.88	8.298%	$221.8809	$221.88	$221.90	$221.90
7 purchase totals =	$1,189.12		$1,278.7888	$1,278.79	$1,278.80	$1,278.80