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	$37.96	3.652%	$39.3463	$39.35	$39.35	$39.30
Purchase #2	$190.68	3.265%	$196.9057	$196.91	$196.90	$196.90
Purchase #3	$119.26	4.133%	$124.189	$124.19	$124.20	$124.20
Purchase #4	$155.59	10.454%	$171.8554	$171.86	$171.85	$171.90
Purchase #5	$165.53	7.601%	$178.1119	$178.11	$178.10	$178.10
Purchase #6	$156.29	9.588%	$171.2751	$171.28	$171.30	$171.30
Purchase #7	$81.44	11.363%	$90.694	$90.69	$90.70	$90.70
7 purchase totals =	$906.75		$972.3774	$972.39	$972.40	$972.40